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Causes of Deafness



Noise-Induced Hearing Loss (NIHL) typically is centered at 3000, 4000, or 6000 Hz. As noise damage progresses, damage starts affecting lower and higher frequencies.

On an audiogram, the resulting configuration has a distinctive notch, sometimes referred to as a “noise notch.” As aging and other effects contribute to higher frequency loss (6-8 kHz on an audiogram), this notch may be obscured and entirely disappear.

Louder sounds cause damage in a shorter period of time. Estimation of a “safe” duration of exposure is possible using an exchange rate of 3 dB. As 3 dB represents a doubling of intensity of sound, duration of exposure must be cut in half to maintain the same energy dose. For example, the “safe” daily exposure amount at 85 dB A, known as an exposure action value, is 8 hours, while the “safe” exposure at 91 dB(A) is only 2 hours (National Institute for Occupational Safety and Health, 1998).


Most 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, transportation, crowds, lawn and maintenance equipment, power tools, gun use, and even hair dryers.


Genetic Deafness



Disease or illness

  • Measles may result in auditory nerve damage
  • Meningitis may damage the auditory nerve or the cochlea
  • Autoimmune disease has only recently been recognized as a potential cause for cochlear damage. Although probably rare, it is possible for autoimmune processes to target the cochlea specifically, without symptoms affecting other organs.Wegener’s granulomatosis is one of the autoimmune conditions that may precipitate hearing loss.
  • AIDS and ARC patients frequently experience auditory system anomalies.



Extremely heavy hydrocodone (Vicodin or Lorcet) abuse is known to cause hearing impairment. Commentators have speculated that radio talk show host Rush Limbaugh’s hearing loss was at least in part caused by his admitted addiction to narcotic pain killers, in particular Vicodin and OxyContin

Exposure to Ototoxic Chemicals

In addition to medications, hearing loss can also result from specific drugs; metals, such as lead; solvents, such as toluene; and asphyxiants. These are mostly industrial chemicals, uncommon in residencies. Combined with noise, these ototoxic chemicals have an additive effect on a person’s hearing loss.


For some ototoxic chemical exposures, particularly styrene,the risk of hearing loss can be higher than being exposed to noise alone. Controlling noise and using hearing protectors are insufficient for preventing hearing loss from these chemicals. However, taking antioxidants helps prevent ototoxic hearing loss, at least to a degree

Physical trauma


Categories of hearing impairment

Hearing loss is categorized by its severity and by the age of onset. Two persons with the same severity of hearing loss will experience it quite differently if it occurs early or late in life. Furthermore, a loss can occur on only one side (unilateral) or on both (bilateral).


As discussed above, there are three major types of hearing loss: neural/sensorineural, conductive, or a combination of both. Treatment depends upon the type of hearing loss that is present.

Quantification of hearing loss

An audiologist conducting an audiometric hearing test in a sound-proof testing booth.

The severity of hearing loss is measured by the degree of loudness, as measured in decibels, a sound must attain before being detected by an individual.

Hearing loss may be ranked as mild, moderate, severe or profound. It is quite common for someone to have more than one degree of hearing loss (i.e. mild sloping to severe).

The following list shows the rankings and their corresponding decibel ranges:

  • Mild:
    • for adults: between 25 and 40 dB
    • for children: between 20 and 40 dB
  • Moderate: between 41 and 55 dB
  • Moderately severe: between 56 and 70 dB
  • Severe: between 71 and 90 dB
  • Profound: 90 dB or greater

The quietest sound one can hear at different frequencies is plotted on an audiogram to reflect one’s ability to hear at different frequencies. The range of normal human hearing (from the softest audible sound to the loudest comfortable sound) is so great that the audiogram must be plotted using a logarithmic scale.

This large normal range, and the different amounts of hearing loss at different frequencies, make it virtually impossible to accurately describe the amount of hearing loss in simple terms such as percentages or the rankings above.

Measuring hearing loss in terms of a percentage is debatable in terms of effectiveness, and has been compared to measuring weight in inches. Though in specific legal situations, where decibels of loss are converted via a recognized legal formula, one can infer a standardized “percentage of hearing loss” which is suitable for legal purposes only.

Another method for determining hearing loss, is the Hearing in Noise Test (HINT). HINT technology was developed by the House Ear Institute, and is intended to measure an ability to understand speech in quiet and noisy environments.


Age of onset of deafness

The age at which the deafness develops is crucial to spoken language acquisition. Post-lingual deafness are far more common than pre-lingual deafness.



Pre-lingual deafness



Post-lingual deafness

Post-lingual deafness where hearing loss is adventitious after the acquisition of speech and language, usually after the age of six. It may develop 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 the people so affected long before the patients themselves will acknowledge the disability. Common treatments include hearing aids and learning lip reading.


People who are hard of hearing have varying amounts of hearing loss but usually not enough to be considered deaf. How people classify themselves relative to hearing loss or deafness is a very personal decision and reflects much more than just their ability to hear.

The phrase hard of hearing, normally used as an adjective, can also be used as a noun, referring to people with hearing impairment as the hard of hearing. People who consider themselves culturally Deaf prefer the term “hard of hearing” or “deaf”, and perceive “hearing impaired” as an insult.

For many people, some of whom are associated with IFHOH, IFHOHYP organizations, the difference between hard of hearing and deaf lies mostly in one’s preference to use oral or sign language. Hard of hearing people prefer oral language alone or sign language derived from (or used together with) oral language. They see deaf people/communities as preferring to use sign language as primary means of communication.

There is, however, often no clear distinction and terminology quite varies between countries or communities, see alternative opinion on “Hard of Hearing”. Additionally also “deafened”, “late-deafened”, “persons with hearing loss/hearing disability” are used.

Hearing impaired persons with partial loss of hearing may find that the quality of their hearing varies from day to day, from one situation to another, or not at all. They may also, to a greater or lesser extent, depend on both hearing aids and lip-reading. They may perhaps not always be aware of it, but they do admit it is important to see the speaker’s face in conversation.

Many people with hearing loss have better hearing in the lower frequency ranges (low tones), and cannot hear as well or at all in the higher frequencies. Some people may merely find it difficult to differentiate between words that begin with consonantal sounds such as the fricatives or sibilants, z, or th, or the plosives d, t, b, or p. They may be unable to hear thin, high-pitched or metallic noises, such as birds chirping or singing, clocks ticking, etc. Often, they are able to hear and understand men’s voices better than women’s.

Others will find their condition much worse if circumstances in their immediate environment affect the way they are able to use their hearing aids, or prevent them from employing their speech reading skills. A room with a high ceiling and a lot of reverberation will affect the sound of a speaker’s voice adversely.

The position of the listener, too, can make a difference; for example, if only the listener’s ineffectual ear is turned towards the speaker, then the listener will have trouble hearing. Difficulties can also arise for the listener trying to lip-read, if the speaker is sitting with his back against the light-source and is in this way obscuring his face. A rule of thumb is that bright lighting is to the hearing-impaired what noise is to the hearing: a source of distraction.

The speaker’s accent; a topic with many potentially unfamiliar words; the softness of his/her voice; a speech impediment; a habit of holding a hand in front of his/her mouth or turning his/her face away at times: all these tendencies cause problems for the hard-of-hearing, especially when they have to rely on lip-reading. Rustling papers and turning pages are the noises that hearing aids pick up first.

Noisy situations are especially difficult, because hearing loss affects not only the ability to hear sounds, but also the ability to localize and filter out background noise.

Unilateral hearing loss

People with unilateral hearing loss (single sided deafness/SSD) can hear typically (or better) in one ear, but have trouble hearing in the other ear. Problems with this type of deficit is inability to localize sounds (ie. unable to tell where traffic is coming from) and inability to process out background noise in a noisy environment, such as in a restaurant.

Social impact

Pre-lingual impairment





Post-lingual impairment




Many relationships can suffer because of emotional conflicts that occur when there are general miscommunications between family members. Generally, it’s not only the person with a hearing disability that feels isolated, but others around them who feel they are not being “heard” or paid attention to, especially when the hearing loss has been gradual.

Many people opt not to choose hearing aids for fear of looking old, since hearing loss is usually associated with old age, which equals ineffectiveness in some societies. Family members then feel as if their hearing loss partner doesn’t care about them enough to make changes to reduce their disability and make it easier to communicate.

Hearing loss in children

12% of children aged 6 – 19 years have permanent hearing damage from excessive noise exposure. The American Academy of Pediatrics advises that children should have their hearing tested several times throughout their schooling:

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


Medical treatments


In addition to hearing aids there exist cochlear implants of increasing complexity and effectiveness. These are useful in treating the mild to profound hearing impairment when the onset follows the acquisitions of language and in some cases in children whose hearing loss came before language was acquired.

Recent research shows variations in efficacy but some studies,show that if implanted at a very young age, some profoundly impaired children can acquire effective hearing and speech, particularly if supported by appropriate rehabilitation such as auditory-verbal therapy

Views of treatments


Many in the culturally Deaf community strongly object to a deaf child being fitted with a cochlear implant (often on the advice of an audiologist; new parents may not have sufficient information on raising deaf children and placed in an oral-only program that emphasizes the ability to speak and listen over other forms of communication such as sign language.


Gene therapy

A 2005 study achieved successful regrowth of cochlea cells in guinea pigs. It is important to note, however, that 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.


Adaptations to hearing impairment

Many hearing impaired individuals use assistive devices in their daily lives:

  • Individuals can communicate by telephone using Telecommunications Device for the Deaf (TDD). These devices look like a typewriters or word processors and transmit typed text over regular telephone lines. Other names in common use are textphone and minicom.
  • Videophones and similar video technologies can be used for distance communication using sign language. Video conferencing technologies permit signed conversations as well as permitting an sign language-English interpreter to voice and sign conversations between a hearing impaired person and that person’s hearing party, negating the use of a TTY device or computer keyboard.
  • Phone captioning is a service in which a hearing person’s speech is captioned by a third party, enabling a hearing impaired person to conduct a conversation with a hearing person over the phone.






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