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How has hearing loss been avoided in war?

How has hearing loss been avoided in war?

Guns are very loud, even in an open field. In a trench or inside a city, I can only imagine they would be louder, and quite capable of causing hearing loss. How have armies ensured that their troops weren't all deaf by the end of the first battle or even bootcamp? I'd imagine cotton balls would help but I've never seen that mentioned in books or other media.

Until the 1940s, it was believed that the cure to loud noises was developing a tolerance to them:

The pervasive attitude of the early 1900s was that hearing loss could be prevented by developing a tolerance to noise. Consequently, any attempts to avoid loud sounds or to protect oneself from them were interpreted as weakness.

Between 1941 and 1944, the US Army finally put this theory to the test:

This “tolerance” theory was scientifically examined in 1941 when the US Army opened the Armored Medical Research Laboratory at Fort Knox, Kentucky. This laboratory completed a landmark study in 1944 resulting in the recommendation that gun crews, gunnery instructors, and others regularly exposed to gunfire blasts be provided hearing-protective devices. The hearing protector of choice was the V-51R, single-flange earplug. Although hearing protection was now being considered, it still was not deemed a requirement.

emphasis added

It wasn't until the advent of the Air Force that hearing protection really became significant:

Even though World War II was a major contributing factor in the evolution of hearing conservation, it was not until after the war that the most significant event occurred. The Army Air Corps became a separate branch of service from the US Army and was renamed the US Air Force. Concurrently, this new branch of service introduced the jet engine aircraft to the military. No sound of that volume and duration had ever before been experienced. It was immediately noted that exposure to jet engine noise caused permanent hearing loss in a brief time. It also made verbal communication impossible and caused a series of physical manifestations described as “ultrasonic sickness.” Symptoms included earache, headache, excessive fatigue, irritability, and feelings of fear. Initially, it was believed that these symptoms were caused by inaudible, ultra-high-frequency sounds being generated by the jet engines. These symptoms, widely reported by air force maintenance crews, triggered a medical study that revealed that the illness was real; however, research attributed it to high levels of audible frequencies.

Finally, the first regulation was established in 1948:

As a result, the US Air Force published the first military regulation on hearing conservation in 1948. AFR 160-3, “Precautionary Measures Against Noise Hazards,” is significant not only because it was the first enforceable regulation in the history of hearing conservation, but it also placed responsibility for the new program on the medical leadership at air force installations. Some of the preventive measures described in AFR 160-3 include limiting noise exposures in terms of overall sound levels and using cotton wads moistened with paraffin as hearing protection for exposures to hazardous noise.

So, for the United States at least, it wasn't until 1948 that preventative measures against the hearing loss of soldiers were really taken seriously.


In Germany Maximilian Negwer founded the company "Fabrik pharmazeutischer und kosmetischer Spezialitäten Max Negwer" in 1907. The first package of Ohropax noise protectors was sold in autumn 1908 for one Goldmark (adjusted for inflation about €5.75).[… ]
In August 1914, the product was recommended by Lieutenant General Freiherr von Dinklage to the War Ministry for use in the military. In 1916 the military introduced Ohropax. This was the first time that large sections of the population got to know the product, making Ohropax noise protectors the company's main product.
Translated from the sources: Wikipedia: Ohropax & Siegeszug von Ohropax begann im Ersten Weltkrieg

These plugs were initially made of wax and reduced the noise by up to 27dB. That would aid somewhat in sleep ability, but compared to noise near a gun of up to 170dB this is obviously a long way from really protecting the health of a hearing system.

This video shows Hermann Göring unplugging these protectors after he landed his plane during the last year of the First World War.

Plain and simple hearing loss and symptoms ranging up to shell shock are listed as reasons for introducing them. Previously it seems that communication ability, even if it required extremest forms of shouting were preferred and just covering the ears with your hands the only option available, despite age old stories about Sirens, Ulysses and wax. Also note that not nearly all troops would have had access to these protectors, exact numbers of plugs delivered being lost.

All this before scientific evidence could be objectively measured:

Even though damage to the inner ear by noise had been demonstrated in the 19th century, otologists could only give approximate estimates of hearing acuity in noise-exposed people, because an accurate and reproducible method of measuring hearing loss was not available until German scientists demonstrated an electronic audiometer in 1919.

In America,

Hearing protection devices (HPDs), used to guard the human ear against incurring hearing loss due to noise, have been in existence at least since the early 1900s [… ] In fact, in 1911, the famous band leader John Phillip Sousa complained to his friend and fellow skeet trapshooter J. A. R. Elliott that shooting traps “took a toll on his ears and was beginning to affect his livelihood [as a musician].” Elliott, being an inventor, then developed and patented (in eight countries, no less), the “Elliott Perfect Ear Protector,” and it became a commercial success (Baldwin 2004).
From: John G. Casali: "Hearing Protection Devices: Regulation, Current Trends, and Emerging Technologies", in: Colleen G. Le Prell et al.: "Noise-Induced Hearing Loss Scientific Advances", Springer, 2012, p 257-283.

Before modern research into noise induced hearing loss started really in the 1940s:

How has hearing loss been avoided in war?

But it really wasn't.

And it really isn't.

VA reported that the 2.5 million veterans receiving disability compensation at the end of fiscal year 2003 had approximately 6.8 million separate disabilities related to their military service (Veterans Benefits Administration, 2004). Disabilities of the auditory system, including tinnitus and hearing loss, were the third most common type, accounting for nearly 10 percent of the total number of disabilities among these veterans.
From: Larry E. Humes et al.: "Noise and Military Service. Implications for Hearing Loss and Tinnitus" 2006.

There are only two realistic options to protect ears from the noise of gunfire: keep away from guns, or don't use them.

A personal experience: as a recruit in the South African Army (1980), I used to be issued disposable wax plugs on range days - well, actually only one. I had to share (a great way for the Army to cut costs - I'm sure they saved millions). I would, under instruction, tear this one plug in two, warm the wax by rolling it in my hands, and stuff my ears with them. Not a great solution - the wax would block all sounds, including the instructions of raging range officers, and it would also attract dirt and dust. So it was quite a mess after a few hours of use. There was also no way of storing it during use: once the packet was opened, it went into your ear, and then into the dust bin. So, we'd wear them to lunch.

Roll forward a few years (1983, or thereabouts), and the Army decided to splurge out on disposable foam plugs. We had to roll these up into tight, thin tubes before inserting, so that the plug could expand in the ear canal. It was a better solution than the wax plugs - except, they were canary yellow. Not great for camouflage.

Being mechanized infantry, when in the turret of my vehicle, I would wear a special helmet with integrated communications - this included muffler-styled ear pieces. This was dead handy, since my 'office' was right next to a 20 mm auto-cannon with a coaxial medium machine gun on the other side of it. Whenever the guns fired, the reports inside the confines of the metal box that was the turret were… well, deafening (without the helmet, it was worse). Even so, I had to remove the helmet before leaving the turret, since the helmet was connected to the communication system by a rather sturdy 'curly cord'. Once outside, it was business as usual for me.

Business as usual was: none of us ever wore ear protection. And here I am today: in spite of 12-years service, I'm as fit as a fiddle with perfect hearing. But is it just me, or do you also hear that ringing noise?

Not exactly primary sources, lol, but Forester & O'Brien are widely regarded to have been sticklers about getting the technical and historical details right in their novels of the Napoleonic era, and the gun crews are depicted as wrapping scarves around their heads (like a "doo rag"), covering their ears for this specific purpose. Not to say these guys were 100% perfect (they both accepted the weevily hard tack myth at face value), but they clearly made an effort way beyond those of most authors of historical fiction and have been lauded by specialized historians for that reason. You see those head rags in a lot of old paintings too.

Auditory injuries are the number one war wound

People with a history of military service have an increased risk of hearing loss. In the United States, 1.5 million military veterans suffer from hearing impairment caused by their time in the services.

Hearing loss is usually associated with age. However, according to Hearing Health Foundation in the U.S., about 60% of younger war veterans who served in Afghanistan and Iraq returned home with hearing loss and/or tinnitus. Although auditory injuries have been called the number one war wound by veterans, the injuries are frequently overlooked.

Regular hearing screenings during service can help diagnose and provide valuable information about hearing loss in the military.

Concentrated doses

The work involves the use of an antioxidant called D-methionine, a component of fermented protein that is found in yoghurt and cheese. The antioxidant, in concentrated doses, has been found to improve some forms of hearing loss and even prevent hearing loss before the exposure to noise. The researchers have already found that the drug can be given up to seven hours after the noise is experienced and still be effective.

"We've been able to show in animal studies that if we give it before and after noise exposure, we can get pretty much full protection from noise-induced hearing loss," the leader of the research team, audiologist Kathleen Campbell, said.

"It doesn't mean it's going to work for long-standing hearing loss, but it does mean that in the early stages, you could intervene and keep it from becoming permanent," she said.

The research will move into determining if even more time can elapse between the drug is given and it still having an effect.

Human clinical trials with the U.S. Army are in the early planning stages, Campbell said.

How do I know if I have hearing loss?

There is no way to know for sure without a completing a hearing test by an audiologist, however, there are some warning signs that may indicate if you have a hearing loss. Ask yourself the following questions and if the answer is to any of the questions, you likely have a hearing loss and should have your hearing evaluated by an audiologist:

  • Do I hear a ringing in my ears or head that is not present in the environment? If the answer is yes, you are experiencing tinnitus, which is highly correlated with hearing loss. (Typically, tinnitus is associated only with hearing loss, but it can be a sign of other health issues or a side effect of medications, so be sure to contact a health professional.)
  • Does it seem as if other people are mumbling? This is a classic sign of hearing loss. Often, when someone has a hearing loss, some sounds of speech are more audible than other sounds, which is perceived as mumbling.
  • Do I hear better out of one ear than another? Normal hearing individuals have the same degree of acuity in each ear. If one ear appears to hear better than the other, that means that at least one ear likely has hearing loss. (Similar to tinnitus, hearing loss in one ear can also be a sign of other health issues and you should consult with a health professional.)
  • Has there been a rapid decline or fluctuation in my hearing? In normal hearing individuals, hearing does not fluctuate very much, if at all, and so this is likely a sign that your hearing is declining. And, if your hearing is fluctuating frequently, you should visit an audiologist or physician relatively soon so as to possibly avoid permanent hearing loss.
  • Have I been exposed to high intensity noise? Frequent exposure to moderately high levels of noise, or, a single instance of very high levels of noise can cause temporary or permanent hearing loss.
  • Is there a history of hearing loss in my family? Some forms of hearing loss are genetic in nature, and if certain family members have or have had hearing loss, you may be at risk yourself.
  • Am I in good health? Heart disease, diabetes, thyroid conditions and side effects of many medications can cause temporary or permanent hearing loss.
  • Am I over 50 years of age? This question should be pretty easy to answer. If the answer is yes, then the chances that you have at least a small degree of hearing loss rises significantly. Most individuals over the age of 70 have at least a mild hearing loss.

Again, the surest way to know if you have a hearing loss, of course, is to have a comprehensive hearing evaluation by a licensed audiologist. Most audiologists participate with insurance carriers and most carriers cover the cost of a hearing test. However, even if you do not have insurance coverage, the cost of a basic hearing test is typically less than $150 and often less than $100.


Since the inner ear is not directly accessible to instruments, identification is by patient report of the symptoms and audiometric testing. Of those who present to their doctor with sensorineural hearing loss, 90% report having diminished hearing, 57% report having a plugged feeling in ear, and 49% report having ringing in ear (tinnitus). About half report vestibular (vertigo) problems.

For a detailed exposition of symptoms useful for screening, a self-assessment questionnaire was developed by the American Academy of Otolaryngology, called the Hearing Handicap Inventory for Adults (HHIA). It is a 25-question survey of subjective symptoms. [1]

Sensorineural hearing loss may be genetic or acquired (i.e. as a consequence of disease, noise, trauma, etc.). People may have a hearing loss from birth (congenital) or the hearing loss may come on later. Many cases are related to old age (age-related).

Genetic Edit

Hearing loss can be inherited. More than 40 genes have been implicated in the cause of deafness. [2] There are 300 syndromes with related hearing loss, and each syndrome may have causative genes.

Recessive, dominant, X-linked, or mitochondrial genetic mutations can affect the structure or metabolism of the inner ear. Some may be single point mutations, whereas others are due to chromosomal abnormalities. Some genetic causes give rise to a late onset hearing loss. Mitochondrial mutations can cause SNHL i.e. m.1555A>G, which makes the individual sensitive to the ototoxic effects of aminoglycoside antibiotics.

  • The most common cause of recessive genetic congenital hearing impairment in developed countries is DFNB1, also known as Connexin 26 deafness or GJB2-related deafness.
  • The most common syndromic forms of hearing impairment include (dominant) Stickler syndrome and Waardenburg syndrome, and (recessive) Pendred syndrome and Usher syndrome.
  • Mitochondrial mutations causing deafness are rare: MT-TL1 mutations cause MIDD (Maternally inherited deafness and diabetes) and other conditions which may include deafness as part of the picture. gene was identified by its association with both congenital and childhood onset autosomal recessive deafness. This gene is expressed in fetal cochleae and many other tissues, and is thought to be involved in the development and maintenance of the inner ear or the contents of the perilymph and endolymph. It was also identified as a tumor associated gene that is overexpressed in ovarian tumors. [3] an inherited neurological disorder with delayed onset that can affect the ears as well as other organs. The hearing loss in this condition is often ANSD (auditory neuropathy spectrum disorder) a neural cause of hearing loss. , a rare inherited autoinflammatory disorder, can lead to hearing loss. : although probably rare, it is possible for autoimmune processes to target the cochlea specifically, without symptoms affecting other organs. Granulomatosis with polyangiitis, an autoimmune condition, may precipitate hearing loss.

Congenital Edit

      , CRS, results from transplacental transmission of the rubella virus during pregnancy. CRS has been controlled by universal vaccination (MMR or MMRV vaccine). (CMV) infection is the most common cause of progressive sensorineural hearing loss in children. It is a common viral infection contracted by contact with infected bodily fluids such as saliva or urine and easily transmitted in nurseries and thus from toddlers to expectant mothers. CMV infection during pregnancy can affect the developing foetus and lead to learning difficulties as well as hearing loss. , a parasitic disease affecting 23% of the population in the U.S., can cause sensorineural deafness to the fetus in utero.

    Presbycusis Edit

    Progressive age-related loss of hearing acuity or sensitivity can start as early as age 18, primarily affecting the high frequencies, and men more than women. [6] Such losses may not become apparent until much later in life. Presbycusis is by far the dominant cause of sensorineural hearing loss in industrialized societies. A study conducted in Sudan, with a population free from loud noise exposures, found significantly less cases of hearing loss when compared with age-matched cases from an industrialized country. [7] Similar findings were reported by a study conducted of a population from Easter island, which reported worse hearing among those that spent time in industrialized countries when compared with those that never left the island. [8] Researchers have argued that factors other than differences in noise exposure, such as genetic make up, might also have contributed to the findings. [9] Hearing loss that worsens with age but is caused by factors other than normal aging, such as noise-induced hearing loss, is not presbycusis, although differentiating the individual effects of multiple causes of hearing loss can be difficult. One in three persons have significant hearing loss by age 65 by age 75, one in two. Age-related hearing loss is neither preventable nor reversible.

    Noise Edit

    Most people living in modern society suffer from some degree of progressive sensorineural (i.e. permanent) noise-induced hearing loss (NIHL) resulting from overloading and damaging the sensory or neural apparatus of hearing in the inner ear. NIHL is typically a drop-out or notch centered at 4000 Hz. Both intensity (SPL) and duration of exposure, and repetitive exposure to unsafe levels of noise contribute to cochlear damage that results in hearing loss. The louder the noise is, the shorter the safe amount of exposure is. NIHL can be either permanent or temporary, called a threshold shift. Unsafe levels of noise can be as little as 70 dB (about twice as loud as normal conversation) if there is prolonged (24-hour) or continuous exposure. 125 dB (a loud rock concert is

    120 dB) is the pain level sounds above this level cause instant and permanent ear damage.

    Noise and ageing are the primary causes of presbycusis, or age-related hearing loss, the most common kind of hearing loss in industrial society. [10] [ citation needed ] The dangers of environmental and occupational noise exposure are widely recognized. Numerous national and international organizations have established standards for safe levels of exposure to noise in industry, the environment, military, transportation, agriculture, mining and other areas. [Note 1] Sound intensity or sound pressure level (SPL) is measured in decibels (dB). For reference:

    db Level Example
    45 dB Ambient noise level around the home
    60 dB Quiet office
    60–65 dB Normal conversation
    70 dB City street noise at 25' [ clarification needed ] or average TV audio
    80 dB Noisy office
    95–104 dB Nightclub dance floor
    120 dB Close-by thunder or a loud rock concert
    150–160 dB Gunshot from a handheld gun

    An increase of 6 dB represents a doubling of the SPL, or energy of the sound wave, and therefore its propensity to cause ear damage. Because human ears hear logarithmically, not linearly, it takes an increase of 10 dB to produce a sound that is perceived to be twice as loud. Ear damage due to noise is proportional to sound intensity, not perceived loudness, so it's misleading to rely on subjective perception of loudness as an indication of the risk to hearing, i.e. it can significantly underestimate the danger.

    While the standards differ moderately in levels of intensity and duration of exposure considered safe, some guidelines can be derived. [Note 2]

    The safe amount of exposure is reduced by a factor of 2 for every exchange rate (3 dB for NIOSH standard or 5 dB for OSHA standard) increase in SPL. For example, the safe daily exposure amount at 85 dB (90 dB for OSHA) is 8 hours, while the safe exposure at 94 dB(A) (nightclub level) is only 1 hour. Noise trauma can also cause a reversible hearing loss, called a temporary threshold shift. This typically occurs in individuals who are exposed to gunfire or firecrackers, and hear ringing in their ears after the event (tinnitus).

    • Ambient environmental noise: Populations living near airports, railyards and train stations, freeways and industrial areas are exposed to levels of noise typically in the 65 to 75 dBA range. If lifestyles include significant outdoor or open window conditions, these exposures over time can degrade hearing. U.S. Dept. of Housing and Urban Development sets standards for noise impact in residential and commercial construction zones. HUD’s noise standards may be found in 24 CFR Part 51, Subpart B. Environmental noise above 65 dB defines a noise-impacted area.
    • Personal audio electronics: Personal audio equipment such as iPods (iPods often reach 115 decibels or higher), can produce powerful enough sound to cause significant NIHL. [11]
    • Acoustic trauma: Exposure to a single event of extremely loud noise (such as explosions) can also cause temporary or permanent hearing loss. A typical source of acoustic trauma is a too-loud music concert.
    • Workplace noise: The OSHA standards 1910.95 General Industry Occupational Noise Exposure and 1926.52 Construction Industry Occupational Noise Exposure identify the level of 90 dB(A) for 8 hour exposure as the level necessary to protect workers from hearing loss.

    Disease or disorder Edit

      Cerebellopontine angle tumour (junction of the pons and cerebellum) – The cerebellopontine angle is the exit site of both the facial nerve(CN7) and the vestibulocochlear nerve(CN8). Patients with these tumors often have signs and symptoms corresponding to compression of both nerves.
        (vestibular schwannoma) – benign neoplasm of Schwann cells affecting the vestibulocochlear nerve – benign tumour of the pia and arachnoid mater
        and ARC patients frequently experience auditory system anomalies. (epidemic parotitis) may result in profound sensorineural hearing loss (90 dB or more), unilaterally (one ear) or bilaterally (both ears). may result in auditory nerve damage but more commonly gives a mixed (sensorineural plus conductive) hearing loss, and can be bilaterally. (herpes zoster oticus)
        is commonly transmitted from pregnant women to their fetuses, and about a third of the infected children will eventually become deaf.

      Ototoxic and neurotoxic drugs and chemicals Edit

      Some over-the-counter as well as prescription drugs and certain industrial chemicals are ototoxic. Exposure to these can result in temporary or permanent hearing loss.

      Some medications cause irreversible damage to the ear, and are limited in their use for this reason. The most important group is the aminoglycosides (main member gentamicin). A rare mitochondrial mutation, m.1555A>G, can increase an individual's susceptibility to the ototoxic effect of aminoglycosides. Long term hydrocodone (Vicodin) abuse is known to cause rapidly progressing sensorineural hearing loss, usually without vestibular symptoms. Methotrexate, a chemotherapy agent, is also known to cause hearing loss. In most cases hearing loss does not recover when the drug is stopped. Paradoxically, methotrexate is also used in the treatment of autoimmune-induced inflammatory hearing loss.

      Various other medications may reversibly degrade hearing. This includes loop diuretics, sildenafil (Viagra), high or sustained dosing of NSAIDs (aspirin, ibuprofen, naproxen, and various prescription drugs: celecoxib, etc.), quinine, and macrolide antibiotics (erythromycin, etc.). Cytotoxic agents such as carboplatinum, used to treat malignancies can give rise to a dose dependent SNHL, as can drugs such as desferrioxamine, used for haematological disorders such as thalassaemia patients prescribed these drugs need to have hearing monitored.

      Prolonged or repeated environmental or work-related exposure to ototoxic chemicals can also result in sensorineural hearing loss. Some of these chemicals are:

        – chemical used recreationally known as 'poppers' – a solvent used as a building block in many organic reactions , an industrial chemical precursor of polystyrene, a plastic , a poisonous gas resulting from incomplete combustion
      • heavy metals: tin, lead, manganese, mercury , an industrial solvent and one of the significant constituents of gasoline , an industrial solvent used in the production of styrene and xylene, highly poisonous petrochemical solvents. Toluene is a component of high-octane gasoline xylene is used in the production of polyester fibers and resins. , an industrial degreasing solvent

      Head trauma Edit

      There can be damage either to the ear itself or to the central auditory pathways that process the information conveyed by the ears. People who sustain head injury are susceptible to hearing loss or tinnitus, either temporary or permanent. Contact sports like football (U.S. NFL), hockey and cricket have a notable incidence of head injuries (concussions). In one survey of retired NFL players, all of whom reported one or more concussions during their playing careers, 25% had hearing loss and 50% had tinnitus. [ citation needed ]

      Perinatal conditions Edit

      These are much more common in premature babies, particularly those under 1500 g at birth. Premature birth can be associated with problems that result in sensorineural hearing loss such as anoxia or hypoxia (poor oxygen levels), jaundice, intracranial haemorrhages, meningitis. Fetal alcohol syndrome is reported to cause hearing loss in up to 64% of infants born to alcoholic mothers, from the ototoxic effect on the developing fetus, plus malnutrition during pregnancy from the excess alcohol intake.

      Iodine deficiency / Hypothyroidism Edit

      Iodine deficiency and endemic hypothyroidism are associated with hearing loss. [12] If a pregnant mother has insufficient iodine intake during pregnancy it affects the development of the inner ear in the foetus leading to sensorineural deafness. This occurs in certain areas of the world, such as the Himalayas, where iodine is deficient in the soil and thus the diet. In these areas there is a high incidence of endemic goitre. This cause of deafness is prevented by adding iodine to salt.

      Brain stroke Edit

      Brain stroke in a region affecting auditory function such as a posterior circulation infarct has been associated with deafness.

      Sensory hearing loss is caused by abnormal structure or function of the hair cells of the organ of Corti in the cochlea. [ disputed – discuss ] Neural hearing impairments are consequent upon damage to the eighth cranial nerve (the vestibulocochlear nerve) or the auditory tracts of the brainstem. If higher levels of the auditory tract are affected this is known as central deafness. Central deafness may present as sensorineural deafness but should be distinguishable from the history and audiological testing.

      Cochlear dead regions in sensory hearing loss Edit

      Hearing impairment may be associated with damage to the hair cells in the cochlea. Sometimes there may be complete loss of function of inner hair cells (IHCs) over a certain region of the cochlea this is called a "dead region". The region can be defined in terms of the range of characteristic frequencies (CFs) of the IHCs and/or neurons immediately adjacent to the dead region.

      Cochlear hair cells Edit

      Outer hair cells (OHCs) contribute to the structure of the Organ of Corti, which is situated between the basilar membrane and the tectorial membrane within the cochlea (See Figure 3). The tunnel of corti, which runs through the Organ of Corti, divides the OHCs and the inner hair cells (IHCs). OHCs are connected to the reticular laminar and the Deiters’ cells. There are roughly twelve thousand OHCs in each human ear, and these are arranged in up to five rows. Each OHC has small tufts of 'hairs', or cilia, on their upper surface known as stereocilia, and these are also arranged into rows which are graded in height. There are approximately 140 stereocilia on each OHC. [13]

      The fundamental role of the OHCs and the IHCs is to function as sensory receptors. The main function of the IHCs is to transmit sound information via afferent neurons. They do this by transducing mechanical movements or signals into neural activity. When stimulated, the stereocilia on the IHCs move, causing a flow of electric current to pass through the hair cells. This electric current creates action potentials within the connected afferent neurons.

      OHCs are different in that they actually contribute to the active mechanism of the cochlea. They do this by receiving mechanical signals or vibrations along the basilar membrane, and transducing them into electrochemical signals. The stereocilia found on OHCs are in contact with the tectorial membrane. Therefore, when the basilar membrane moves due to vibrations, the stereocilia bend. The direction in which they bend, dictates the firing rate of the auditory neurons connected to the OHCs. [14]

      The bending of the stereocilia towards the basal body of the OHC causes excitation of the hair cell. Thus, an increase in firing rate of the auditory neurons connected to the hair cell occurs. On the other hand, the bending of the stereocilia away from the basal body of the OHC causes inhibition of the hair cell. Thus, a decrease in firing rate of the auditory neurons connected to the hair cell occurs. OHCs are unique in that they are able to contract and expand (electromotility). Therefore, in response to the electrical stimulations provided by the efferent nerve supply, they can alter in length, shape and stiffness. These changes influence the response of the basilar membrane to sound. [13] [14] It is therefore clear that the OHCs play a major role in the active processes of the cochlea. [13] The main function of the active mechanism is to finely tune the basilar membrane, and provide it with a high sensitivity to quiet sounds. The active mechanism is dependent on the cochlea being in good physiological condition. However, the cochlea is very susceptible to damage. [14]

      Hair cell damage Edit

      SNHL is most commonly caused by damage to the OHCs and the IHCs. [ disputed – discuss ] There are two methods by which they might become damaged. Firstly, the entire hair cell might die. Secondly, the stereocilia might become distorted or destroyed. Damage to the cochlea can occur in several ways, for example by viral infection, exposure to ototoxic chemicals, and intense noise exposure. Damage to the OHCs results in either a less effective active mechanism, or it may not function at all. OHCs contribute to providing a high sensitivity to quiet sounds at a specific range of frequencies (approximately 2–4 kHz). Thus, damage to the OHCs results in the reduction of sensitivity of the basilar membrane to weak sounds. Amplification to these sounds is therefore required, in order for the basilar membrane to respond efficiently. IHCs are less susceptible to damage in comparison to the OHCs. However, if they become damaged, this will result in an overall loss of sensitivity. [14]

      Neural tuning curves Edit

      Frequency selectivity Edit

      The traveling wave along the basilar membrane peaks at different places along it, depending on whether the sound is low or high frequency. Due to the mass and stiffness of the basilar membrane, low frequency waves peak in the apex, while high frequency sounds peak in the basal end of the cochlea. [13] Therefore, each position along the basilar membrane is finely tuned to a particular frequency. These specifically tuned frequencies are referred to as characteristic frequencies (CF). [14]

      If a sound entering the ear is displaced from the characteristic frequency, then the strength of response from the basilar membrane will progressively lessen. The fine tuning of the basilar membrane is created by the input of two separate mechanisms. The first mechanism being a linear passive mechanism, which is dependent on the mechanical structure of the basilar membrane and its surrounding structures. The second mechanism is a non-linear active mechanism, which is primarily dependent on the functioning of the OHCs, and also the general physiological condition of the cochlea itself. The base and apex of the basilar membrane differ in stiffness and width, which cause the basilar membrane to respond to varying frequencies differently along its length. The base of the basilar membrane is narrow and stiff, resulting in it responding best to high frequency sounds. The apex of the basilar membrane is wider and much less stiff in comparison to the base, causing it to respond best to low frequencies. [14]

      This selectivity to certain frequencies can be illustrated by neural tuning curves. These demonstrate the frequencies a fiber responds to, by showing threshold levels (dB SPL) of auditory nerve fibers as a function of different frequencies. This demonstrates that auditory nerve fibers respond best, and hence have better thresholds at the fiber's characteristic frequency and frequencies immediately surrounding it. The basilar membrane is said to be ‘sharply tuned’ due to the sharp ‘V’ shaped curve, with its ‘tip’ centered at the auditory fibers characteristic frequency. This shape shows how few frequencies a fiber responds to. If it were a broader ‘V’ shape, it would be responding to more frequencies (See Figure 4). [13]

      IHC vs OHC hearing loss Edit

      A normal neural tuning curve is characterised by a broadly tuned low frequency ‘tail’, with a finely tuned middle frequency ‘tip’. However, where there is partial or complete damage to the OHCs, but with unharmed IHCs, the resulting tuning curve would show the elimination of sensitivity at the quiet sounds. I.e. where the neural tuning curve would normally be most sensitive (at the ‘tip’) (See Figure 5). [14]

      Where both the OHCs and the IHCs are damaged, the resulting neural tuning curve would show the elimination of sensitivity at the ‘tip'. However, due to IHC damage, the whole tuning curve becomes raised, giving a loss of sensitivity across all frequencies (See Figure 6). It is only necessary for the first row of OHCs to be damaged for the elimination of the finely tuned ‘tip’ to occur. This supports the idea that the incidence of OHC damage and thus a loss of sensitivity to quiet sounds, occurs more than IHC loss. [14]

      When the IHCs or part of the basilar membrane are damaged or destroyed, so that they no longer function as transducers, the result is a ‘dead region’. Dead regions can be defined in terms of the characteristic frequencies of the IHC, related to the specific place along the basilar membrane where the dead region occurs. Assuming that there has been no shift in the characteristic frequencies relating to certain regions of the basilar membrane, due to the damage of OHCs. This often occurs with IHC damage. Dead regions can also be defined by the anatomical place of the non-functioning IHC (such as an “apical dead region”), or by the characteristic frequencies of the IHC adjacent to the dead region. [15]

      Dead region audiometry Edit

      Pure tone audiometry (PTA) Edit

      Dead regions affect audiometric results, but perhaps not in the way expected. For example, it may be expected that thresholds would not be obtained at the frequencies within the dead region, but would be obtained at frequencies adjacent to the dead region. Therefore, assuming normal hearing exists around the dead region, it would produce an audiogram that has a dramatically steep slope between the frequency where a threshold is obtained, and the frequency where a threshold cannot be obtained due to the dead region. [15]

      However, it appears that this is not the case. Dead regions cannot be clearly found via PTA audiograms. This may be because although the neurons innervating the dead region, cannot react to vibration at their characteristic frequency. If the basilar membrane vibration is large enough, neurons tuned to different characteristic frequencies such as those adjacent to the dead region, will be stimulated due to the spread of excitation. Therefore, a response from the patient at the test frequency will be obtained. This is referred to as “off-place listening”, and is also known as ‘off-frequency listening’. This will lead to a false threshold being found. Thus, it appears a person has better hearing than they actually do, resulting in a dead region being missed. Therefore, using PTA alone, it is impossible to identify the extent of a dead region (See Figure 7 and 8). [15]

      Consequently, how much is an audiometric threshold affected by a tone with its frequency within a dead region? This depends on the location of the dead region. Thresholds at low frequency dead regions, are more inaccurate than those at higher frequency dead regions. This has been attributed to the fact that excitation due to vibration of the basilar membrane spreads upwards from the apical regions of the basilar membrane, more than excitation spreads downwards from higher frequency basal regions of the cochlea. This pattern of the spread of excitation is similar to the ‘upward spread of masking’ phenomenon. If the tone is sufficiently loud to produce enough excitation at the normally functioning area of the cochlea, so that it is above that areas threshold. The tone will be detected, due to off-frequency listening which results in a misleading threshold. [15]

      To help to overcome the issue of PTA producing inaccurate thresholds within dead regions, masking of the area beyond the dead region that is being stimulated can be used. This means that the threshold of the responding area is sufficiently raised, so that it cannot detect the spread of excitation from the tone. This technique has led to the suggestion that a low frequency dead region may be related to a loss of 40-50 dB. [16] [17] However, as one of the aims of PTA is to determine whether or not there is a dead region, it may be difficult to assess which frequencies to mask without the use of other tests. [15]

      Based on research it has been suggested that a low frequency dead region may produce a relatively flat loss, or a very gradually sloping loss towards the higher frequencies. As the dead region will be less detectable due to the upward spread of excitation. Whereas, there may be a more obvious steeply sloping loss at high frequencies for a high frequency dead region. Although it is likely that the slope represents the less pronounced downward spread of excitation, rather than accurate thresholds for those frequencies with non-functioning hair cells. Mid-frequency dead regions, with a small range, appear to have less effect on the patient’s ability to hear in everyday life, and may produce a notch in the PTA thresholds. [15] Although it is clear that PTA is not the best test to identify a dead region. [18]

      Psychoacoustic tuning curves (PTC) and threshold equalizing noise (TEN) tests Edit

      Although some debate continues regarding the reliability of such tests, [19] it has been suggested [ weasel words ] that psychoacoustic tuning curves (PTCs) and threshold-equalising noise (TEN) results may be useful in detecting dead regions, rather than PTA. PTCs are similar to neural tuning curves. They illustrate the level of a masker (dB SPL) tone at threshold, as a function of deviation from center frequency (Hz). [13] They are measured by presenting a fixed low intensity pure tone while also presenting a narrow-band masker, with a varying center frequency. The masker level is varied, so that the level of masker needed to just mask the test signal is found for the masker at each center frequency. The tip of the PTC is where the masker level needed to just mask the test signal is the lowest. For normal hearing people this is when the masker center frequency is closest to the frequency of the test signal (See Figure 9). [18]

      In the case of dead regions, when the test signal lies within the boundaries of a dead region, the tip of the PTC will be shifted to the edge of the dead region, to the area that is still functioning and detecting the spread of excitation from the signal. In the case of a low frequency dead region, the tip is shifted upwards indicating a low frequency dead region starting at the tip of the curve. For a high frequency dead region, the tip is shifted downwards from the signal frequency to the functioning area below the dead region. [18] However, the traditional method of obtaining PTCs is not practical for clinical use, and it has been argued [ weasel words ] that TENs are not accurate enough. [18] [19] A fast method for finding PTCs has been developed and it may provide the solution. However, more research to validate this method is required, before it can be accepted clinically.

      Perceptual consequences of a dead region Edit

      Audiogram configurations are not good indicators of how a dead region will affect a person functionally, mainly due to individual differences. [14] For example, a sloping audiogram is often present with a dead region, due to the spread of excitation. However, the individual may well be affected differently from someone with a corresponding sloped audiogram caused by partial damage to hair cells rather than a dead region. They will perceive sounds differently, yet the audiogram suggests that they have the same degree of loss. Huss and Moore investigated how hearing impaired patients perceive pure tones, and found that they perceive tones as noisy and distorted, more (on average) than a person without a hearing impairment. However, they also found that the perception of tones as being like noise, was not directly related to frequencies within the dead regions, and was therefore not an indicator of a dead region. This therefore suggests that audiograms, and their poor representation of dead regions, are inaccurate predictors of a patient’s perception of pure tone quality. [20]

      Research by Kluk and Moore has shown that dead regions may also affect the patient’s perception of frequencies beyond the dead regions. There is an enhancement in the ability to distinguish between tones that differ very slightly in frequency, in regions just beyond the dead regions compared to tones further away. An explanation for this may be that cortical re-mapping has occurred. Whereby, neurons which would normally be stimulated by the dead region, have been reassigned to respond to functioning areas near it. This leads to an over-representation of these areas, resulting in an increased perceptual sensitivity to small frequency differences in tones. [21]

      Vestibulocochlear nerve pathology Edit

      • congenital deformity of the internal auditory canal,
      • neoplastic and pseudo-neoplastic lesions, with special detailed emphasis on schwannoma of the eighth cranial nerve (acoustic neuroma),
      • non-neoplastic Internal Auditory Canal/CerebelloPontine Angle pathology, including vascular loops,

      Case history Edit

      Before examination, a case history provides guidance about the context of the hearing loss.

      • major concern
      • pregnancy and childbirth information
      • medical history
      • development history
      • family history

      Otoscopy Edit

      Direct examination of the external canal and tympanic membrane (ear drum) with an otoscope, a medical device inserted into the ear canal that uses light to examine the condition of the external ear and tympanic membrane, and middle ear through the semi-translucent membrane.

      Differential testing Edit

      Differential testing is most useful when there is unilateral hearing loss, and distinguishes conductive from sensorineural loss. These are conducted with a low frequency tuning fork, usually 512 Hz, and contrast measures of air and bone conducted sound transmission.

        , in which a tuning fork is touched to the midline of the forehead, localizes to the normal ear in people with unilateral sensorineural hearing loss. , which tests air conduction vs. bone conduction is positive, because both bone and air conduction are reduced equally.
      • less common Bing and Schwabach variants of the Rinne test.
      • absolute bone conduction (ABC) test.

      Table 1. A table comparing sensorineural to conductive hearing loss

      Criteria Sensorineural hearing loss Conductive hearing loss
      Anatomical site Inner ear, cranial nerve VIII, or central processing centers Middle ear (ossicular chain), tympanic membrane, or external ear
      Weber test Sound localizes to normal ear in unilateral SNHL Sound localizes to affected ear (ear with conductive loss) in unilateral cases
      Rinne test Positive Rinne air conduction > bone conduction (both air and bone conduction are decreased equally, but the difference between them is unchanged). Negative Rinne bone conduction > air conduction (bone/air gap)

      Other, more complex, tests of auditory function are required to distinguish the different types of hearing loss. Bone conduction thresholds can differentiate sensorineural hearing loss from conductive hearing loss. Other tests, such as oto-acoustic emissions, acoustic stapedial reflexes, speech audiometry and evoked response audiometry are needed to distinguish sensory, neural and auditory processing hearing impairments.

      Tympanometry Edit

      A tympanogram is the result of a test with a tympanometer. It tests the function of the middle ear and mobility of the eardrum. It can help identify conductive hearing loss due to disease of the middle ear or eardrum from other kinds of hearing loss including SNHL.

      Audiometry Edit

      An audiogram is the result of a hearing test. The most common type of hearing test is pure tone audiometry (PTA). It charts the thresholds of hearing sensitivity at a selection of standard frequencies between 250 and 8000 Hz. There is also high frequency pure tone audiometry which tests frequencies from 8000-20,000 Hz. PTA can be used to differentiate between conductive hearing loss, sensorineural hearing loss and mixed hearing loss. A hearing loss can be described by its degree i.e. mild, moderate, severe or profound, or by its shape i.e. high frequency or sloping, low frequency or rising, notched, U-shaped or 'cookie-bite', peaked or flat.

      There are also other kinds of audiometry designed to test hearing acuity rather than sensitivity (speech audiometry), or to test auditory neural pathway transmission (evoked response audiometry).

      Magnetic resonance imaging Edit

      MRI scans can be used to identify gross structural causes of hearing loss. They are used for congenital hearing loss when changes to the shape of the inner ear or nerve of hearing may help diagnosis of the cause of the hearing loss. They are also useful in cases where a tumour is suspected or to determine the degree of damage in a hearing loss caused by bacterial infection or auto-immune disease. Scanning is of no value in age-related deafness.

      Presbycusis is the leading cause of SNHL and is progressive and nonpreventable, and at this time, we do not have either somatic or gene therapy to counter heredity-related SNHL. But other causes of acquired SNHL are largely preventable, especially nosocusis type causes. This would involve avoiding environmental noise, and traumatic noise such as rock concerts and nightclubs with loud music. Use of noise attenuation measures like ear plugs is an alternative, as well as learning about the noise levels one is exposed to. Currently, several accurate sound level measurement apps exist. Reducing exposure time can also help manage risk from loud exposures.

      Treatment modalities fall into three categories: pharmacological, surgical, and management. As SNHL is a physiologic degradation and considered permanent, there are as of this time, no approved or recommended treatments.

      There have been significant advances in identification of human deafness genes and elucidation of their cellular mechanisms as well as their physiological function in mice. [22] [23] Nevertheless, pharmacological treatment options are very limited and clinically unproven. [24] Such pharmaceutical treatments as are employed are palliative rather than curative, and addressed to the underlying cause if one can be identified, in order to avert progressive damage.

      Profound or total hearing loss may be amenable to management by cochlear implants, which stimulate cochlear nerve endings directly. A cochlear implant is surgical implantation of a battery powered electronic medical device in the inner ear. Unlike hearing aids, which make sounds louder, cochlear implants do the work of damaged parts of the inner ear (cochlea) to provide sound signals to the brain. These consist of both internal implanted electrodes and magnets and external components. [25] The quality of sound is different than natural hearing but may enable the recipient to better recognize speech and environmental sounds. Because of risk and expense, such surgery is reserved for cases of severe and disabling hearing impairment

      Management of sensorineural hearing loss involves employing strategies to support existing hearing such as lip-reading, enhanced communication etc. and amplification using hearing aids. Hearing aids are specifically tuned to the individual hearing loss to give maximum benefit.

      Pharmaceuticals Edit

        vitamins – Researchers at the University of Michigan report that a combination of high doses of vitamins A, C, and E, and Magnesium, taken one hour before noise exposure and continued as a once-daily treatment for five days, was very effective at preventing permanent noise-induced hearing loss in animals. [26] – a brand name for an international prescription drug extract of Ginkgo biloba. It is classified as a vasodilator. Among its research uses is treatment of sensorineural deafness and tinnitus presumed to be of vascular origin. – a substance similar to a vitamin, with antioxidant properties. It is made in the body, but levels fall with age. [Note 3] , a synthetic drug molecule that mimics glutathione peroxidase (GPx), a critical enzyme in the inner ear that protects it from damage caused by loud sounds or noise [27]

      Stem cell and gene therapy Edit

      Hair cell regeneration using stem cell and gene therapy is years or decades away from being clinically feasible. [28] However, studies are currently underway on the subject, with the first FDA-approved trial beginning in February 2012. [29]

      Sudden sensorineural hearing loss (SSHL or SSNHL), commonly known as sudden deafness, occurs as an unexplained, rapid loss of hearing—usually in one ear—either at once or over several days. Nine out of ten people with SSHL lose hearing in only one ear. It should be considered a medical emergency. Delaying diagnosis and treatment may render treatment less effective or ineffective.

      Experts estimate that SSHL strikes one person per 100 every year, typically adults in their 40s and 50s. The actual number of new cases of SSHL each year could be much higher because the condition often goes undiagnosed.

      Presentation Edit

      Many people notice that they have SSHL when they wake up in the morning. Others first notice it when they try to use the deafened ear, such as when they use a phone. Still others notice a loud, alarming "pop" just before their hearing disappears. People with sudden deafness often become dizzy, have ringing in their ears (tinnitus), or both.

      Diagnosis Edit

      SSHL is diagnosed via pure tone audiometry. If the test shows a loss of at least 30 dB in three adjacent frequencies, the hearing loss is diagnosed as SSHL. For example, a hearing loss of 30 dB would make conversational speech sound more like a whisper.

      Causes Edit

      Only 10 to 15 percent of the cases diagnosed as SSHL have an identifiable cause. Most cases are classified as idiopathic, also called sudden idiopathic hearing loss (SIHL) and idiopathic sudden sensorineural hearing loss (ISSHL or ISSNHL) [30] [31] The majority of evidence points to some type of inflammation in the inner ear as the most common cause of SSNHL.

        – The swelling may be due to a virus. A herpes type virus is believed to be the most common cause of sudden sensorineural hearing loss. The herpes virus lies dormant in our bodies and reactivates for an unknown reason.
      • Vascular ischemia of the inner ear or cranial nerve VIII (CN8) , usually due to a rupture of the round or oval windows and the leakage of perilymph. The patient will usually also experience vertigo or imbalance. A history of trauma is usually present and changes to hearing or vertigo occur with alteration in intracranial pressure such as with straining lifting, blowing etc. – can be due to an autoimmune illness such as systemic lupus erythematosus, granulomatosis with polyangiitis

      Treatment Edit

      Hearing loss completely recovers in around 35-39% of patients with SSNHL, usually within one to two weeks from onset. [32] Eighty-five percent of those who receive treatment from an otolaryngologist (sometimes called an ENT surgeon) will recover some of their hearing.

        and antioxidants (Betaserc), an anti-vertigo drug [33] agents that reduce blood viscosity (such as hydroxyethyl starch, dextran and pentoxifylline) [34] agents, primarily oral corticosteroids such as prednisone, methylprednisone [citation needed]
      • Intratympanic administration – Gel formulations are under investigation to provide more consistent drug delivery to the inner ear. [35] Local drug delivery can be accomplished through intratympanic administration, a minimally invasive procedure where the ear drum is anesthetized and a drug is administered into the middle ear. From the middle ear, a drug can diffuse across the round window membrane into the inner ear. [35] Intratympanic administration of steroids may be effective for sudden sensorineural hearing loss for some patients, but high quality clinical data has not been generated. [36] Intratympanic administration of an anti-apoptotic peptide (JNK inhibitor) is currently being evaluated in late-stage clinical development. [37]

      Epidemiology Edit

      General hearing loss affects close to 10% of the global population. [38] In the United States alone, it is expected that 13.5 million Americans suffer from sensorineural hearing loss. Of those afflicted with sensorineural hearing loss, approximately 50% are congenitally related. The other 50% are due to maternal or fetal infections, post-natal infections, viral infections due to rubella or cytomegalovirus, ototoxic drugs, [39] exposure to loud sounds, severe head trauma, and premature births [40]

      Of the genetically related sensorineural hearing loss cases, 75% are autosomal recessive, 15-20% autosomal dominant, and 1-3% sex-linked. While the specific gene and protein is still unknown, mutations in the connexin 26 gene near the DFNB1 locus of chromosome 13 [41] are thought to account for most of the autosomal recessive genetic-related sensorineural hearing loss [40]

      At least 8.5 per 1000 children younger than age 18 have sensorineural hearing loss. General hearing loss is proportionally related to age. At least 314 per 1000 people older than age 65 have hearing loss. Several risk factors for sensorineural hearing loss have been studied over the past decade. Osteoporosis, stapedectomy surgery, pneumococcal vaccinations, mobile phone users, and hyperbilirubinemia at birth are among some of the known risk factors.

      Learn More

      Presented by AudiologyOnline in partnership with the Defense Hearing Center of Excellence and supported by the Department of Veterans Affairs and the Department of Defense

      Dates: June 4, 11, 18, and 25, 2014

      Purpose: To address an audience of providers across the country who are seeing patients that present with a constellation of complaints after experiencing exposure to a blast, but not necessarily suffering an injury that they are aware of currently.

      Auditory injuries are so prevalent among veterans that they have been called "the No. 1 war wound."

      Moreover, unlike in the general population where hearing loss is more common in older individuals, auditory injuries are startlingly common among younger veterans who have served in Afghanistan and Iraq. According to the Hearing Health Foundation, 60% of veterans who served in Afghanistan and Iraq returned home with hearing loss and/or tinnitus.

      Yet, because auditory injuries are often not readily apparent, they are frequently overlooked.

      The Soldier's Life

      Modern military life is noisy.

      In addition to noise typically found in civilian life -- cars, machines, loud music -- soldiers are also faced with military-specific auditory insults.

      Military-grade weapons are "often louder and more damaging to the ears than standard sportsman-type weapons," said Col. Mark Packer, MD, director of the Department of Defense's Hearing Center of Excellence. "The transport systems we use to move troops and equipment are much louder than their civilian counterparts. We also put folks in environments where we have to use generators to make electricity, so we have people living next to generators. There are also unexpected, impact noises from blasts and combat."

      Both chronic and acute noise exposure can damage enlisted personnel's hearing, and it's not uncommon to see veterans whose hearing has been degraded both by chronic and acute noise exposure. Acute auditory events -- such as the explosion of an improvised explosive device -- can cause sudden dramatic changes in hearing and may get more attention than auditory injuries that occur over time.

      But, unfortunately, even acute auditory injuries can be overlooked because blast exposures result in other serious, obvious, and potentially life-threatening injuries. In that scenario hearing often becomes a low priority concern.

      The uniformed services are, however, trying to diagnose -- and possibly prevent -- auditory injuries with a robust hearing health program that emphasizes screening, education, and hearing protection.

      In 2009, the Department of Defense established the Hearing Center of Excellence, which "deals with everything from prevention through rehabilitation for every case of hearing loss and auditory injury," Packer said. "We're also working to develop a registry system that will be used to encourage and facilitate the conduct of research, the development of best practices, and the development of educational tools."

      Consistent and regular auditory screening is an important part of the program. Ideally, members will undergo a baseline audiogram at the start of service. Audiograms will be repeated at least annually, or more often, depending on members' occupational exposure. Audiograms and other hearing screenings will also be performed as needed. ("If someone has hearing symptoms, intervention at that time provides documentation of the injury, as well as an opportunity to give education and recommend appropriate levels of hearing protection," Packer said.) An exit audiogram, performed at the end of service, will document the effect of service on any particular service member's hearing.

      After Discharge

      Because many veterans seek healthcare outside of the VA medical system, all primary care providers should assess all patients for a history of military service, regardless of age, sex, or gender. Ask veterans about the details of their service:

      Where did they serve? When? What kind of work did they do? Did they suffer any acute or chronic auditory injuries or assaults?

      These details may provide insights into their auditory health -- but be careful of generalizations based on service history. According to a 2010 epidemiological study reported in the American Journal of Preventive Medicine, general officers and executives, enlisted trainees and scientists and professionals reported higher rates of noise-induced hearing injuries (NIHI) than infantry and gun crews.

      Although the AJPM authors note that "this finding may indicate under-reporting of NIHI among combat arms and equipment repair occupations," it's important to remember that all veterans -- even those who worked far from the front lines -- are at risk of auditory injury.

      Create individually-tailored auditory screening programs based on veterans' current auditory health and past medical history. (Need help obtaining military medical records? Contact the nearest VA medical center.) At a minimum, "screening for high-frequency sounds should be standard protocol for any primary care physician working with veterans," said Joseph Pellegrino, AuD, CCC-A, audiology clinic director at Syracuse University. Patients who don't pass a basic screening, as well as those who have known or suspected hearing issues, should be referred to audiology for further evaluation.

      Note, however, that a normal audiogram, or audiogram records that demonstrate a return to baseline thresholds after an injury, do not necessarily mean the absence of hearing impairment. New research suggests that noise exposures cause cochlear neuronal degeneration, which can cause hearing loss, hyperacusis, and tinnitus. "Threshold recovery does not mean hearing recovery," said M. Charles Liberman, PhD, director of Eaton-Peabody Laboratories at Massachusetts Eye and Ear Infirmary, who believes that auditory injuries may be cumulative, in much the same way head concussions can cause brain damage over time. "Your thresholds can go back to normal, but probably every time this happens, you're losing a few neurons."

      While there is currently no way to restore hearing, great strides have been made in hearing technology. "Hearing aids are starting to become kind of cool," Pellegrino said. "Some hearing aids now have Bluetooth connectivity you can pair your hearing aids to your iPhone and answer your phone or listen to music wirelessly through your hearing aids. If you ask Siri for directions, she can speak directly to you through your hearing aids."

      FDA-approved middle ear implants and cochlear implantation are options for veterans with profound hearing loss.

      "We live in a time when there are a lot of technological advances and devices. There's a solution for just about everybody out there," Packer said. Adequately assessing, protecting, and rehabilitating our veterans' hearing will increase their quality of life and ease their transition to civilian life.

      Sudden Hearing Loss: Don’t Ignore This Ear Emergency

      For most people, hearing loss happens gradually over time. You probably don’t notice changes in your hearing from one day to the next.

      Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

      But sometimes, hearing loss can come on suddenly and without warning.

      This is called sudden sensorineural hearing loss, or sudden hearing loss. It’s when someone loses hearing — usually just in one ear — over the course of three days or less. It can happen to anyone but is most common in adults in their 40s and 50s.

      While it can be easy to brush off a sudden change in your hearing (maybe my ear is just clogged or it’s my allergies acting up), it’s actually very important to see a doctor right away if this happens.

      “There are not many emergencies of the ear, but this is one thing that we would consider an emergency,” says ear surgeon Erika Woodson, MD.

      There can be other causes of sudden changes to your hearing, but if it is SSNHL, it needs treatment — and the sooner, the better.

      SSNHL vs. other ear issues

      Sudden sensorineural hearing loss is different from the common temporary phenomenon called eustachian tube dysfunction. This is the cloudy hearing and full feeling in the ear that you might experience when traveling on an airplane. It’s also different from a feeling of blockage caused by allergies or a cold, though it can feel similar.

      SSNHL happens because of damage to the inner ear, or because of problems with the nerve fibers that deliver information from the ear to the brain. Most of the time, there’s no clear rhyme or reason why it happens to someone. It can be either temporary or permanent.

      So, if you experience a sudden change in your hearing, how do you know whether it’s SSNHL or one of these other things?

      Any kind of noticeable hearing loss should prompt a visit to your primary care doctor or urgent care center for investigation, Dr. Woodson says.

      The presence of dizziness or vertigo along with hearing loss can be clues of SSNHL, she says. Some people also report a strong ringing in their ear before their hearing fades.

      “That’s because the brain does not know what to do with the changes of signal it’s getting from the ear, so it either misinterprets what bad signal it’s getting as noise, or it’s trying to fill in the gap — almost like a phantom sound,” she explains.

      An ENT can help get to the bottom of the problem

      If a primary care or urgent care provider doesn’t see any signs of blockage or infection in the ear that could be causing sudden hearing loss, the next step is quick referral to an ear, nose and throat specialist.

      The ENT specialist will want to rule out anything else that could be causing the symptoms and give a hearing test.

      “Many of these patients would not have a baseline hearing test for comparison, but in those circumstances, what we’re mostly looking for is asymmetry, or a difference between the two ears,” Dr. Woodson explains.

      They may also order an MRI to rule out other problems, such as benign tumors that form on the hearing and balance nerves. These are called acoustic neuromas. “These are uncommon tumors, but this is the way they tend to pop up first, with sudden hearing loss,” Dr. Woodson says.

      If SSNHL is determined to be the culprit for the hearing loss, the next step is steroid therapy to reduce inflammation in the inner ear. This typically starts with oral treatment (pills), but depending on the situation and the patient, injection of steroids into the ear drum could also be an option.

      Does hearing come back?

      Studies have found that half to two-thirds of people who experience SSNHL recover their hearing. Those who don’t may benefit from other treatments such as hearing aids or cochlear implants.

      While there isn’t necessarily a way to predict who will and who will not get their full hearing back, Dr. Woodson notes that people with only mild hearing loss who seek treatment within a week tend to have higher rates of recovery.

      In the same vein, it’s hard to know who is going to experience sudden hearing loss in the first place. But Dr. Woodson says recent research has uncovered associations between SSNHL and vascular risk factors such as high cholesterol, diabetes and hypertension.

      “Anything that can affect the little blood vessels coursing through our body can make somebody more likely to have sudden sensorineural hearing loss,” she says.

      So the best thing people can do to avoid it? “Take care of themselves and their chronic medical problems,” Dr. Woodson says. “All the things that are important for heart health are important for ear health as well.”

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      Warning: Toys to avoid

      The U.S. League for the Hard of Hearing warns against loud toys. If it is loud, hurts your ears or causes ringing in them, do not buy it.

      Here are examples of baby and infant toys to avoid for the sake of your small children's hearing:

      • Certain rattles and squeaky toys are measured at sound levels as high as 110 dB (comparable to a power tool in the playroom).
      • Musical toys, such as electric guitars, drums and horns, emit sounds as loud as 120 dB.
      • Toy phones for small children have been measured between 123 and 129 dB.
      • Toys designed to amplify the voice are measured at up to 135 dB (comparable to a jetliner at take-off).
      • Toys producing firearm sounds emit volumes as loud as 150 dB one foot away from the noise source (causing physical pain).

      Prolonged exposure to these noise levels will cause irreversible hearing damage, and even brief exposure carries a risk of permanent harm.

      How do we hear?

      The auditory system
      (Source: NIH/NIDCD)

      Hearing depends on a series of events that change sound waves in the air into electrical signals. Your auditory nerve then carries these signals to your brain through a complex series of steps.

      1. Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum.
      2. The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes.
      3. The bones in the middle ear couple the sound vibrations from the air to fluid vibrations in the cochlea of the inner ear, which is shaped like a snail and filled with fluid. An elastic partition runs from the beginning to the end of the cochlea, splitting it into an upper and lower part. This partition is called the basilar membrane because it serves as the base, or ground floor, on which key hearing structures sit.
      4. Once the vibrations cause the fluid inside the cochlea to ripple, a traveling wave forms along the basilar membrane. Hair cells-sensory cells sitting on top of the basilar membrane-ride the wave.
      5. As the hair cells move up and down, microscopic hair-like projections (known as stereocilia) that perch on top of the hair cells bump against an overlying structure and bend. Bending causes pore-like channels, which are at the tips of the stereocilia, to open up. When that happens, chemicals rush into the cells, creating an electrical signal.
      6. The auditory nerve carries this electrical signal to the brain, which turns it into a sound that we recognize and understand.

      This animated video illustrates how sounds travel from the ear to the brain, where they are interpreted and understood. View Journey of Sound to the Brain, a video produced by the National Institute on Deafness and Other Communication Disorders.

      Why am I losing my hearing?

      Hearing loss happens for different reasons. Many people lose their hearing slowly as they age. This condition is known as presbycusis (prez-buh-KYOO-sis). Doctors do not know why presbycusis affects some people more than others, but it seems to run in families. Another reason for hearing loss with aging may be years of exposure to loud noise. This condition is known as noise-induced hearing loss. Many construction workers, farmers, musicians, airport workers, landscapers, and people in the military have hearing loss even in their younger and middle years because of exposure to loud noises.

      Hearing loss can also be caused by viral or bacterial infections, heart conditions, stroke, head injuries, tumors, and certain medicines.

      What should I do if I have trouble hearing?

      Hearing loss can be serious. The most important thing you can do if you think you have a hearing loss is to seek advice from a health care provider. There are several types of professionals who can help you. You might want to start with your primary care physician, an otolaryngologist, an audiologist, or a hearing aid specialist. Each has a different type of training and expertise. Each can be an important part of your hearing health care. If you are told there is nothing that can be done about your hearing loss, seek a second opinion.

      • An otolaryngologist (oh-toe-lair-in-GAH-luh-jist) is a doctor who specializes in diagnosing and treating diseases of the ear, nose, throat, and neck. An otolaryngologist, sometimes called an ENT, will try to find out why you’re having trouble hearing and offer treatment options. He or she might also refer you to another hearing professional, such as an audiologist.
      • An audiologist (aw-dee-AH-luh-jist) has specialized training in identifying and measuring the type and degree of hearing loss. Some audiologists are licensed to fit hearing aids.
      • A hearing aid specialist is someone who is licensed by your state to conduct and evaluate basic hearing tests, offer counseling, and fit and test hearing aids.

      What treatments and devices can help?

      Your treatment will depend on the degree of your hearing loss, so some treatments will work better for you than others. There are a number of devices and aids that help you hear better when you have hearing loss. Here are the most common ones:

        are electronic instruments worn in or behind your ear. They make sounds louder. To find the hearing aid that works best for you, you might have to try more than one. Be sure to ask for a trial period with your hearing aid and understand the terms and conditions of the trial period. Work with your hearing aid provider until you are comfortable putting on and removing the hearing aid, adjusting the volume level, and changing the batteries. Hearing aids are generally not covered by health insurance companies, although some do. Medicare does not cover hearing aids for adults however, diagnostic evaluations are covered if they are ordered by a physician for the purpose of assisting the physician in developing a treatment plan.
      • Cochlear implants. Cochlear (COKE-lee-ur) implants are small electronic devices surgically implanted in the inner ear that help provide a sense of sound to people with more severe-to-profound hearing loss. Cochlear implants can be recommended for one or both ears.
      • Bone anchored hearing systems bypass the ear canal and middle ear and are designed to use your body’s natural ability to transfer sound through bone conduction. The sound processor picks up sound, converts it into vibrations, and then relays the vibrations through your skull bone to your inner ear. include phone amplifying devices, captioned phones, smart phone or tablet apps. Other systems for larger areas can be hearing loops, FM, or infrared systems in places of worship, theaters, and auditoriums.
      • Lipreading or speechreading is often used to augment a hearing aid or cochlear implant to help people with hearing loss follow conversations. People who use this method pay close attention to others when they talk by watching the speaker’s mouth and body movements. Special trainers can help you learn how to lipread or speechread.

      Can my friends and family help me?

      You and your family can work together to make living with hearing loss easier. Here are some things you can do:

      • Tell your friends and family about your hearing loss. The more friends and family you tell, the more people there will be to help you cope with your hearing loss.
      • Ask others to face you when they talk so that you can see their faces. If you watch their faces move and see their expressions, it might help you to understand them better.
      • Ask people to speak louder, but not shout. Tell them they do not have to talk slowly, just more clearly.
      • Turn off the TV or the radio when you aren’t actively listening to it.
      • Be aware of noise around you that can make hearing more difficult. When you go to a restaurant, for example, don’t sit near the kitchen or near a band playing music. Background noise makes it hard to hear people talk.

      Working together to hear better may be tough on everyone for a while. It will take time for you to get used to watching people as they talk and for people to get used to speaking lslowly and clearly. Be patient and continue to work together. Hearing better is worth the effort.

      Interesting Facts about Hearing Loss

      • Hearing loss is the third most common physical condition after arthritis and heart disease.
      • Gradual hearing loss can affect people of all ages — varying from mild to profound. Depending on the cause, it can be mild or severe, temporary or permanent.
      • Degrees of hearing loss: mild, moderate, severe, profound.
      • Congenital hearing loss means you are born without hearing.
      • Hearing loss is an invisible condition. Since hearing loss is often not visible, people might jump to the wrong conclusion that someone is aloof, confused, not smart, or has had a personality change.
      • Noise and aging are the most common causes of hearing loss in adults. There is a strong relationship between age and reported hearing loss.
      • Presbycusis, or age-related hearing loss, causes changes in the inner ear as you get older resulting in a slow but steady hearing loss. In older people, a hearing loss is often confused with, or complicates, conditions such as dementia.
      • Noise-induced hearing loss may happen suddenly or gradually. Being exposed to everyday noises such as listening to loud music, being in a noisy work environment, or using a lawn mower can lead to hearing loss over many years.
      • Sudden, noise-induced hearing loss from gunfire and explosions is the number one disability caused by combat in current wars.
      • More often than not, severe tinnitus (ringing in the ears) will accompany hearing loss and may be just as debilitating as hearing loss itself


      • About 2 to 3 out of every 1,000 children in the United States are born with a detectable level of hearing loss in one or both ears. 1
      • More than 90 percent of deaf children are born to hearing parents. 2
      • Approximately 15 percent of American adults (37.5 million) aged 18 and over report some trouble hearing. 3
      • Among adults aged 20-69, the overall annual prevalence of hearing loss dropped slightly from 16 percent (28.0 million) in the 1999-2004 period to 14 percent (27.7 million) in the 2011–2012 period. 4
      • Age is the strongest predictor of hearing loss among adults aged 20-69, with the greatest amount of hearing loss in the 60 to 69 age group. 4
      • Men are almost twice as likely as women to have hearing loss among adults aged 20-69. 4
      • Non-Hispanic white adults are more likely than adults in other racial/ethnic groups to have hearing loss non-Hispanic black adults have the lowest prevalence of hearing loss among adults aged 20-69. 4
      • About 18 percent of adults aged 20-69 have speech-frequency hearing loss in both ears from among those who report 5 or more years of exposure to very loud noise at work, as compared to 5.5 percent of adults with speech-frequency hearing loss in both ears who report no occupational noise exposure. 4
      • One in eight people in the United States (13 percent, or 30 million) aged 12 years or older has hearing loss in both ears, based on standard hearing examinations. 5
      • About 2 percent of adults aged 45 to 54 have disabling hearing loss. The rate increases to 8.5 percent for adults aged 55 to 64. Nearly 25 percent of those aged 65 to 74 and 50 percent of those who are 75 and older have disabling hearing loss. 6
      • Roughly 10 percent of the U.S. adult population, or about 25 million Americans, has experienced tinnitus lasting at least five minutes in the past year. 7
      • About 28.8 million U.S. adults could benefit from using hearing aids. 8
      • Among adults aged 70 and older with hearing loss who could benefit from hearing aids, fewer than one in three (30 percent) has ever used them. Even fewer adults aged 20 to 69 (approximately 16 percent) who could benefit from wearing hearing aids have ever used them. 9
      • As of December 2012, approximately 324,200 cochlear implants have been implanted worldwide. In the United States, roughly 58,000 devices have been implanted in adults and 38,000 in children. 10
      • Five out of 6 children experience ear infection (otitis media) by the time they are 3 years old. 11


      • Hearing loss is defined as diminished acuity to sounds which would otherwise be heard normally. [15] The terms hearing impaired or hard of hearing are usually reserved for people who have relative inability to hear sound in the speech frequencies. The severity of hearing loss is categorized according to the increase in intensity of sound above the usual level required for the listener to detect it.
      • Deafness is defined as a degree of loss such that a person is unable to understand speech, even in the presence of amplification. [15] In profound deafness, even the highest intensity sounds produced by an audiometer (an instrument used to measure hearing by producing pure tone sounds through a range of frequencies) may not be detected. In total deafness, no sounds at all, regardless of amplification or method of production, can be heard. is another aspect of hearing which involves the perceived clarity of a word rather than the intensity of sound made by the word. In humans, this is usually measured with speech discrimination tests, which measure not only the ability to detect sound, but also the ability to understand speech. There are very rare types of hearing loss that affect speech discrimination alone. One example is auditory neuropathy, a variety of hearing loss in which the outer hair cells of the cochlea are intact and functioning, but sound information is not faithfully transmitted by the auditory nerve to the brain. [22]

      Use of the terms "hearing impaired", "deaf-mute", or "deaf and dumb" to describe deaf and hard of hearing people is discouraged by many in the deaf community as well as advocacy organizations, as they are offensive to many deaf and hard of hearing people. [23] [24]

      Hearing standards Edit

      Human hearing extends in frequency from 20 to 20,000 Hz, and in intensity from 0 dB to 120 dB HL or more. 0 dB does not represent absence of sound, but rather the softest sound an average unimpaired human ear can hear some people can hear down to −5 or even −10 dB. Sound is generally uncomfortably loud above 90 dB and 115 dB represents the threshold of pain. The ear does not hear all frequencies equally well: hearing sensitivity peaks around 3,000 Hz. There are many qualities of human hearing besides frequency range and intensity that cannot easily be measured quantitatively. However, for many practical purposes, normal hearing is defined by a frequency versus intensity graph, or audiogram, charting sensitivity thresholds of hearing at defined frequencies. Because of the cumulative impact of age and exposure to noise and other acoustic insults, 'typical' hearing may not be normal. [25] [26]

      • difficulty using the telephone
      • loss of sound localization
      • difficulty understanding speech, especially of children and women whose voices are of a higher frequency.
      • difficulty understanding speech in the presence of background noise (cocktail party effect)
      • sounds or speech sounding dull, muffled or attenuated
      • need for increased volume on television, radio, music and other audio sources

      Hearing loss is sensory, but may have accompanying symptoms:

      There may also be accompanying secondary symptoms:

        , heightened sensitivity with accompanying auditory pain to certain intensities and frequencies of sound, sometimes defined as "auditory recruitment" , ringing, buzzing, hissing or other sounds in the ear when no external sound is present and disequilibrium , also known as autophonia, abnormal hearing of one's own voice and respiratory sounds, usually as a result of a patulous (a constantly open) eustachian tube or dehiscent superior semicircular canals
      • disturbances of facial movement (indicating a possible tumour or stroke) or in persons with Bell's palsy

      Complications Edit

      Hearing loss is associated with Alzheimer's disease and dementia. [27] The risk increases with the hearing loss degree. There are several hypotheses including cognitive resources being redistributed to hearing and social isolation from hearing loss having a negative effect. [28] According to preliminary data, hearing aid usage can slow down the decline in cognitive functions. [29]

      Hearing loss is responsible for causing thalamocortical dysrthymia in the brain which is a cause for several neurological disorders including tinnitus and visual snow syndrome.

      Cognitive decline Edit

      Hearing loss is an increasing concern especially in aging populations, the prevalence of hearing loss increase about two-fold for each decade increase in age after age 40. [30] While the secular trend might decrease individual level risk of developing hearing loss, the prevalence of hearing loss is expected to rise due to the aging population in the US. Another concern about aging process is cognitive decline, which may progress to mild cognitive impairment and eventually dementia. [31] The association between hearing loss and cognitive decline has been studied in various research settings. Despite the variability in study design and protocols, the majority of these studies have found consistent association between age-related hearing loss and cognitive decline, cognitive impairment, and dementia. [32] The association between age-related hearing loss and Alzheimer's disease was found to be nonsignificant, and this finding supports the hypothesis that hearing loss is associated with dementia independent of Alzheimer pathology. [32] There are several hypothesis about the underlying causal mechanism for age-related hearing loss and cognitive decline. One hypothesis is that this association can be explained by common etiology or shared neurobiological pathology with decline in other physiological system. [33] Another possible cognitive mechanism emphasize on individual's cognitive load. As people developing hearing loss in the process of aging, the cognitive load demanded by auditory perception increases, which may lead to change in brain structure and eventually to dementia. [34] One other hypothesis suggests that the association between hearing loss and cognitive decline is mediated through various psychosocial factors, such as decrease in social contact and increase in social isolation. [33] Findings on the association between hearing loss and dementia have significant public health implication, since about 9% of dementia cases can be attributed to hearing loss. [35]

      Falls Edit

      Falls have important health implications, especially for an aging population where they can lead to significant morbidity and mortality. Elderly people are particularly vulnerable to the consequences of injuries caused by falls, since older individuals typically have greater bone fragility and poorer protective reflexes. [36] Fall-related injury can also lead to burdens on the financial and health care systems. [36] In literature, age-related hearing loss is found to be significantly associated with incident falls. [37] There is also a potential dose-response relationship between hearing loss and falls---greater severity of hearing loss is associated with increased difficulties in postural control and increased prevalence of falls. [38] The underlying causal link between the association of hearing loss and falls is yet to be elucidated. There are several hypotheses that indicate that there may be a common process between decline in auditory system and increase in incident falls, driven by physiological, cognitive, and behavioral factors. [38] This evidence suggests that treating hearing loss has potential to increase health-related quality of life in older adults. [38]

      Depression Edit

      Depression is one of the leading causes of morbidity and mortality worldwide. In older adults, the suicide rate is higher than it is for younger adults, and more suicide cases are attributable to depression. [39] Different studies have been done to investigate potential risk factors that can give rise to depression in later life. Some chronic diseases are found to be significantly associated with risk of developing depression, such as coronary heart disease, pulmonary disease, vision loss and hearing loss. [40] Hearing loss can attribute to decrease in health-related quality of life, increase in social isolation and decline in social engagement, which are all risk factors for increased risk of developing depression symptoms. [41]

      Spoken language ability Edit

      Post-lingual deafness is hearing loss that is sustained after the acquisition of language, which can occur due to disease, trauma, or as a side-effect of a medicine. Typically, hearing loss is gradual and often detected by family and friends of affected individuals long before the patients themselves will acknowledge the disability. [42] Post-lingual deafness is far more common than pre-lingual deafness. Those who lose their hearing later in life, such as in late adolescence or adulthood, face their own challenges, living with the adaptations that allow them to live independently.

      Prelingual deafness is profound hearing loss that is sustained before the acquisition of language, which can occur due to a congenital condition or through hearing loss before birth or in early infancy. Prelingual deafness impairs an individual's ability to acquire a spoken language in children, but deaf children can acquire spoken language through support from cochlear implants (sometimes combined with hearing aids). [43] [44] Non-signing (hearing) parents of deaf babies (90–95% of cases) usually go with oral approach without the support of sign language, as these families lack previous experience with sign language and cannot competently provide it to their children without learning it themselves. Unfortunately, this may in some cases (late implantation or not sufficient benefit from cochlear implants) bring the risk of language deprivation for the deaf baby [45] because the deaf baby would not have a sign language if the child is unable to acquire spoken language successfully. The 5–10% of cases of deaf babies born into signing families have the potential of age-appropriate development of language due to early exposure to a sign language by sign-competent parents, thus they have the potential to meet language milestones, in sign language in lieu of spoken language. [46]

      Hearing loss has multiple causes, including ageing, genetics, perinatal problems and acquired causes like noise and disease. For some kinds of hearing loss the cause may be classified as of unknown cause.

      There is a progressive loss of ability to hear high frequencies with aging known as presbycusis. For men, this can start as early as 25 and women at 30. Although genetically variable it is a normal concomitant of ageing and is distinct from hearing losses caused by noise exposure, toxins or disease agents. [47] Common conditions that can increase the risk of hearing loss in elderly people are high blood pressure, diabetes, or the use of certain medications harmful to the ear. [48] [49] While everyone loses hearing with age, the amount and type of hearing loss is variable. [50]

      Noise-induced hearing loss (NIHL), also known as acoustic trauma, typically manifests as elevated hearing thresholds (i.e. less sensitivity or muting). Noise exposure is the cause of approximately half of all cases of hearing loss, causing some degree of problems in 5% of the population globally. [51] The majority of hearing loss is not due to age, but due to noise exposure. [52] Various governmental, industry and standards organizations set noise standards. [53] Many people are unaware of the presence of environmental sound at damaging levels, or of the level at which sound becomes harmful. Common sources of damaging noise levels include car stereos, children's toys, motor vehicles, crowds, lawn and maintenance equipment, power tools, gun use, musical instruments, and even hair dryers. Noise damage is cumulative all sources of damage must be considered to assess risk. In the US, 12.5% of children aged 6–19 years have permanent hearing damage from excessive noise exposure. [54] The World Health Organization estimates that half of those between 12 and 35 are at risk from using personal audio devices that are too loud. [11] Hearing loss in adolescents may be caused by loud noise from toys, music by headphones, and concerts or events. [55]

      Hearing loss can be inherited. Around 75–80% of all these cases are inherited by recessive genes, 20–25% are inherited by dominant genes, 1–2% are inherited by X-linked patterns, and fewer than 1% are inherited by mitochondrial inheritance. [56] Syndromic deafness occurs when there are other signs or medical problems aside from deafness in an individual, [56] such as Usher syndrome, Stickler syndrome, Waardenburg syndrome, Alport's syndrome, and neurofibromatosis type 2. Nonsyndromic deafness occurs when there are no other signs or medical problems associated with the deafness in an individual. [56]

      Fetal alcohol spectrum disorders are reported to cause hearing loss in up to 64% of infants born to alcoholic mothers, from the ototoxic effect on the developing fetus plus malnutrition during pregnancy from the excess alcohol intake. Premature birth can be associated with sensorineural hearing loss because of an increased risk of hypoxia, hyperbilirubinaemia, ototoxic medication and infection as well as noise exposure in the neonatal units. Also, hearing loss in premature babies is often discovered far later than a similar hearing loss would be in a full-term baby because normally babies are given a hearing test within 48 hours of birth, but doctors must wait until the premature baby is medically stable before testing hearing, which can be months after birth. [57] The risk of hearing loss is greatest for those weighing less than 1500 g at birth.

      Some medications may reversibly affect hearing. These medications are considered ototoxic. This includes loop diuretics such as furosemide and bumetanide, non-steroidal anti-inflammatory drugs (NSAIDs) both over-the-counter (aspirin, ibuprofen, naproxen) as well as prescription (celecoxib, diclofenac, etc.), paracetamol, quinine, and macrolide antibiotics. [65] Others may cause permanent hearing loss. [66] The most important group is the aminoglycosides (main member gentamicin) and platinum based chemotherapeutics such as cisplatin and carboplatin. [67] [68]

      In addition to medications, hearing loss can also result from specific chemicals in the environment: metals, such as lead solvents, such as toluene (found in crude oil, gasoline [69] and automobile exhaust, [69] for example) and asphyxiants. [70] Combined with noise, these ototoxic chemicals have an additive effect on a person's hearing loss. [70] Hearing loss due to chemicals starts in the high frequency range and is irreversible. It damages the cochlea with lesions and degrades central portions of the auditory system. [70] For some ototoxic chemical exposures, particularly styrene, [71] the risk of hearing loss can be higher than being exposed to noise alone. The effects is greatest when the combined exposure include impulse noise. [72] [73] A 2018 informational bulletin by the US Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) introduces the issue, provides examples of ototoxic chemicals, lists the industries and occupations at risk and provides prevention information. [74]

      There can be damage either to the ear, whether the external or middle ear, to the cochlea, or to the brain centers that process the aural information conveyed by the ears. Damage to the middle ear may include fracture and discontinuity of the ossicular chain. Damage to the inner ear (cochlea) may be caused by temporal bone fracture. People who sustain head injury are especially vulnerable to hearing loss or tinnitus, either temporary or permanent. [75] [76]

      Sound waves reach the outer ear and are conducted down the ear canal to the eardrum, causing it to vibrate. The vibrations are transferred by the 3 tiny ear bones of the middle ear to the fluid in the inner ear. The fluid moves hair cells (stereocilia), and their movement generates nerve impulses which are then taken to the brain by the cochlear nerve. [77] [78] The auditory nerve takes the impulses to the brainstem, which sends the impulses to the midbrain. Finally, the signal goes to the auditory cortex of the temporal lobe to be interpreted as sound. [79]

      Hearing loss is most commonly caused by long-term exposure to loud noises, from recreation or from work, that damage the hair cells, which do not grow back on their own. [80] [81] [9]

      Older people may lose their hearing from long exposure to noise, changes in the inner ear, changes in the middle ear, or from changes along the nerves from the ear to the brain. [82]

      Identification of a hearing loss is usually conducted by a general practitioner medical doctor, otolaryngologist, certified and licensed audiologist, school or industrial audiometrist, or other audiometric technician. Diagnosis of the cause of a hearing loss is carried out by a specialist physician (audiovestibular physician) or otorhinolaryngologist.

      Hearing loss is generally measured by playing generated or recorded sounds, and determining whether the person can hear them. Hearing sensitivity varies according to the frequency of sounds. To take this into account, hearing sensitivity can be measured for a range of frequencies and plotted on an audiogram. Other method for quantifying hearing loss is a hearing test using a mobile application or hearing aid application, which includes a hearing test. [83] [84] Hearing diagnosis using mobile application is similar to the audiometry procedure. [83] Audiogram, obtained using mobile application, can be used to adjust hearing aid application. [84] Another method for quantifying hearing loss is a speech-in-noise test. which gives an indication of how well one can understand speech in a noisy environment. [85] Otoacoustic emissions test is an objective hearing test that may be administered to toddlers and children too young to cooperate in a conventional hearing test. Auditory brainstem response testing is an electrophysiological test used to test for hearing deficits caused by pathology within the ear, the cochlear nerve and also within the brainstem.

      A case history (usually a written form, with questionnaire) can provide valuable information about the context of the hearing loss, and indicate what kind of diagnostic procedures to employ. Examinations include otoscopy, tympanometry, and differential testing with the Weber, Rinne, Bing and Schwabach tests. In case of infection or inflammation, blood or other body fluids may be submitted for laboratory analysis. MRI and CT scans can be useful to identify the pathology of many causes of hearing loss.

      Hearing loss is categorized by severity, type, and configuration. Furthermore, a hearing loss may exist in only one ear (unilateral) or in both ears (bilateral). Hearing loss can be temporary or permanent, sudden or progressive. The severity of a hearing loss is ranked according to ranges of nominal thresholds in which a sound must be so it can be detected by an individual. It is measured in decibels of hearing loss, or dB HL. There are three main types of hearing loss: conductive hearing loss, sensorineural hearing loss, and mixed hearing loss. [15] An additional problem which is increasingly recognised is auditory processing disorder which is not a hearing loss as such but a difficulty perceiving sound. The shape of an audiogram shows the relative configuration of the hearing loss, such as a Carhart notch for otosclerosis, 'noise' notch for noise-induced damage, high frequency rolloff for presbycusis, or a flat audiogram for conductive hearing loss. In conjunction with speech audiometry, it may indicate central auditory processing disorder, or the presence of a schwannoma or other tumor.

      People with unilateral hearing loss or single-sided deafness (SSD) have difficulty in hearing conversation on their impaired side, localizing sound, and understanding speech in the presence of background noise. One reason for the hearing problems these patients often experience is due to the head shadow effect. [86]

      It is estimated that half of cases of hearing loss are preventable. [87] About 60% of hearing loss in children under the age of 15 can be avoided. [2] A number of preventive strategies are effective including: immunization against rubella to prevent congenital rubella syndrome, immunization against H. influenza and S. pneumoniae to reduce cases of meningitis, and avoiding or protecting against excessive noise exposure. [15] The World Health Organization also recommends immunization against measles, mumps, and meningitis, efforts to prevent premature birth, and avoidance of certain medication as prevention. [88] World Hearing Day is a yearly event to promote actions to prevent hearing damage.

      Noise exposure is the most significant risk factor for noise-induced hearing loss that can be prevented. [89] [ citation needed ] Different programs exist for specific populations such as school-age children, adolescents and workers. [90] Education regarding noise exposure increases the use of hearing protectors. [91] The use of antioxidants is being studied for the prevention of noise-induced hearing loss, particularly for scenarios in which noise exposure cannot be reduced, such as during military operations. [92]

      Workplace noise regulation Edit

      Noise is widely recognized as an occupational hazard. In the United States, the National Institute for Occupational Safety and Health (NIOSH) and the Occupational Safety and Health Administration (OSHA) work together to provide standards and enforcement on workplace noise levels. [93] [94] The hierarchy of hazard controls demonstrates the different levels of controls to reduce or eliminate exposure to noise and prevent hearing loss, including engineering controls and personal protective equipment (PPE). [95] Other programs and initiative have been created to prevent hearing loss in the workplace. For example, the Safe-in-Sound Award was created to recognize organizations that can demonstrate results of successful noise control and other interventions. [96] Additionally, the Buy Quiet program was created to encourage employers to purchase quieter machinery and tools. [97] By purchasing less noisy power tools like those found on the NIOSH Power Tools Database and limiting exposure to ototoxic chemicals, great strides can be made in preventing hearing loss. [98]

      Companies can also provide personal hearing protector devices tailored to both the worker and type of employment. Some hearing protectors universally block out all noise, and some allow for certain noises to be heard. Workers are more likely to wear hearing protector devices when they are properly fitted. [99]

      Often interventions to prevent noise-induced hearing loss have many components. A 2017 Cochrane review found that stricter legislation might reduce noise levels. [100] Providing workers with information on their sound exposure levels was not shown to decrease exposure to noise. Ear protection, if used correctly, can reduce noise to safer levels, but often, providing them is not sufficient to prevent hearing loss. Engineering noise out and other solutions such as proper maintenance of equipment can lead to noise reduction, but further field studies on resulting noise exposures following such interventions are needed. Other possible solutions include improved enforcement of existing legislation and better implementation of well-designed prevention programmes, which have not yet been proven conclusively to be effective. The conclusion of the Cochrane Review was that further research could modify what is now regarding the effectiveness of the evaluated interventions. [100]

      The Institute for Occupational Safety and Health of the German Social Accident Insurance has created a hearing impairment calculator based on the ISO 1999 model for studying threshold shift in relatively homogeneous groups of people, such as workers with the same type of job. The ISO 1999 model estimates how much hearing impairment in a group can be ascribed to age and noise exposure. The result is calculated via an algebraic equation that uses the A-weighted sound exposure level, how many years the people were exposed to this noise, how old the people are, and their sex. The model’s estimations are only useful for people without hearing loss due to non-job related exposure and can be used for prevention activities. [101]

      Screening Edit

      The American Academy of Pediatrics advises that children should have their hearing tested several times throughout their schooling: [54]

      • When they enter school
      • At ages 6, 8, and 10
      • At least once during middle school
      • At least once during high school

      While the American College of Physicians indicated that there is not enough evidence to determine the utility of screening in adults over 50 years old who do not have any symptoms, [102] the American Language, Speech Pathology and Hearing Association recommends that adults should be screened at least every decade through age 50 and at 3-year intervals thereafter, to minimize the detrimental effects of the untreated condition on quality of life. [103] For the same reason, the US Office of Disease Prevention and Health Promotion included as one of Healthy People 2020 objectives: to increase the proportion of persons who have had a hearing examination. [104]

      Management depends on the specific cause if known as well as the extent, type and configuration of the hearing loss. Sudden hearing loss due to and underlying nerve problem may be treated with corticosteroids. [105]

      Most hearing loss, that resulting from age and noise, is progressive and irreversible, and there are currently no approved or recommended treatments. A few specific kinds of hearing loss are amenable to surgical treatment. In other cases, treatment is addressed to underlying pathologies, but any hearing loss incurred may be permanent. Some management options include hearing aids, cochlear implants, assistive technology, and closed captioning. [9] This choice depends on the level of hearing loss, type of hearing loss, and personal preference. Hearing aid applications are one of the options for hearing loss management. [84] For people with bilateral hearing loss, it is not clear if bilateral hearing aids (hearing aids in both ears) are better than a unilateral hearing aid (hearing aid in one ear). [9]

      Globally, hearing loss affects about 10% of the population to some degree. [51] It caused moderate to severe disability in 124.2 million people as of 2004 (107.9 million of whom are in low and middle income countries). [13] Of these 65 million acquired the condition during childhood. [15] At birth

      3 per 1000 in developed countries and more than 6 per 1000 in developing countries have hearing problems. [15]

      Hearing loss increases with age. In those between 20 and 35 rates of hearing loss are 3% while in those 44 to 55 it is 11% and in those 65 to 85 it is 43%. [8]

      A 2017 report by the World Health Organization estimated the costs of unaddressed hearing loss and the cost-effectiveness of interventions, for the health-care sector, for the education sector and as broad societal costs. [106] Globally, the annual cost of unaddressed hearing loss was estimated to be in the range of $750–790 billion international dollars.

      The International Organization for Standardization (ISO) developed the ISO 1999 standards for the estimation of hearing thresholds and noise-induced hearing impairment. [107] They used data from two noise and hearing study databases, one presented by Burns and Robinson (Hearing and Noise in Industry, Her Majesty's Stationery Office, London, 1970) and by Passchier-Vermeer (1968). [108] As race are some of the factors that can affect the expected distribution of pure-tone hearing thresholds several other national or regional datasets exist, from Sweden, [109] Norway, [110] South Korea, [111] the United States [112] and Spain. [113]

      In the United States hearing is one of the health outcomes measure by the National Health and Nutrition Examination Survey (NHANES), a survey research program conducted by the National Center for Health Statistics. It examines health and nutritional status of adults and children in the United States. Data from the United States in 2011-2012 found that rates of hearing loss has declined among adults aged 20 to 69 years, when compared with the results from an earlier time period (1999-2004). It also found that adult hearing loss is associated with increasing age, sex, ethnicity, educational level, and noise exposure. [114] Nearly one in four adults had audiometric results suggesting noise-induced hearing loss. Almost one in four adults who reported excellent or good hearing had a similar pattern (5.5% on both sides and 18% on one side). Among people who reported exposure to loud noise at work, almost one third had such changes. [115]

      People with extreme hearing loss may communicate through sign languages. Sign languages convey meaning through manual communication and body language instead of acoustically conveyed sound patterns. This involves the simultaneous combination of hand shapes, orientation and movement of the hands, arms or body, and facial expressions to express a speaker's thoughts. "Sign languages are based on the idea that vision is the most useful tool a deaf person has to communicate and receive information". [116]

      Deaf culture refers to a tight-knit cultural group of people whose primary language is signed, and who practice social and cultural norms which are distinct from those of the surrounding hearing community. This community does not automatically include all those who are clinically or legally deaf, nor does it exclude every hearing person. According to Baker and Padden, it includes any person or persons who "identifies him/herself as a member of the Deaf community, and other members accept that person as a part of the community," [117] an example being children of deaf adults with normal hearing ability. It includes the set of social beliefs, behaviors, art, literary traditions, history, values, and shared institutions of communities that are influenced by deafness and which use sign languages as the main means of communication. [118] [119] Members of the Deaf community tend to view deafness as a difference in human experience rather than a disability or disease. [120] [121] When used as a cultural label especially within the culture, the word deaf is often written with a capital D and referred to as "big D Deaf" in speech and sign. When used as a label for the audiological condition, it is written with a lower case d. [118] [119]

      Stem cell transplant and gene therapy Edit

      A 2005 study achieved successful regrowth of cochlea cells in guinea pigs. [122] However, the regrowth of cochlear hair cells does not imply the restoration of hearing sensitivity, as the sensory cells may or may not make connections with neurons that carry the signals from hair cells to the brain. A 2008 study has shown that gene therapy targeting Atoh1 can cause hair cell growth and attract neuronal processes in embryonic mice. Some hope that a similar treatment will one day ameliorate hearing loss in humans. [123]

      Recent research, reported in 2012 achieved growth of cochlear nerve cells resulting in hearing improvements in gerbils, [124] using stem cells. Also reported in 2013 was regrowth of hair cells in deaf adult mice using a drug intervention resulting in hearing improvement. [125] The Hearing Health Foundation in the US has embarked on a project called the Hearing Restoration Project. [126] Also Action on Hearing Loss in the UK is also aiming to restore hearing. [127]

      Researchers reported in 2015 that genetically deaf mice which were treated with TMC1 gene therapy recovered some of their hearing. [128] [129] In 2017, additional studies were performed to treat Usher syndrome [130] and here, a recombinant adeno-associated virus seemed to outperform the older vectors. [131] [132]

      Audition Edit

      Besides research studies seeking to improve hearing, such as the ones listed above, research studies on the deaf have also been carried out in order to understand more about audition. Pijil and Shwarz (2005) conducted their study on the deaf who lost their hearing later in life and, hence, used cochlear implants to hear. They discovered further evidence for rate coding of pitch, a system that codes for information for frequencies by the rate that neurons fire in the auditory system, especially for lower frequencies as they are coded by the frequencies that neurons fire from the basilar membrane in a synchronous manner. Their results showed that the subjects could identify different pitches that were proportional to the frequency stimulated by a single electrode. The lower frequencies were detected when the basilar membrane was stimulated, providing even further evidence for rate coding. [133]