Hearing loss

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This article is about the medical condition. For other uses, see Deaf (disambiguation).
Hearing loss
International Symbol for Deafness.jpg
The international symbol of deafness and hard of hearing
Classification and external resources
ICD-10 H90H91
ICD-9 389
MedlinePlus 003044
eMedicine article/994159
MeSH D034381

Hearing loss, also known as hard of hearing, anacusis, or hearing impairment, is a partial or total inability to hear.[1] It may occur in one or both ears.[2] In children hearing problems can affect the ability to learn language and in adults it can cause work related difficulties.[3] In some people, particularly older people, hearing loss result in loneliness. Deafness is typically used to refer to those with no or only little hearing.[2]

Hearing loss may be caused by a number of factors, including: genetics, old age, exposure to noise, some infections, birth complications, trauma to the ear, and certain medications or toxins. A common infection that results in hearing loss is chronic ear infections. Certain infections during pregnancy such as rubella may also cause problems.> Hearing loss is diagnosed when hearing testing finds that a person is unable to hear 25 decibels in at least one ear.[2] Testing for poor hearing is recommended for all newborns.[3] Hearing loss can be categorised as as mild, moderate, severe, or profound.[2]

Half of hearing loss is preventable. This includes by immunization, proper care around pregnancy, avoiding loud noise, and avoiding certain medications.[2] The World Health Organization recommends that young people limit the use of personal audio players to an hour a day in an effort to limit exposure to noise.[4] Early identification and support are particularly important in children. For many hearing aids, sign language, cochlear implants and subtitles are useful. Lip reading is another useful skill many develop. Access to hearing aids; however, is limited in many areas of the world.[2]

Globally hearing loss affects about 10% of the population to some degree.[5] It causes disability in 5% (360 to 538 million) and moderate to severe disability in 124 million people.[2][6][7] Of those with moderate to severe disability 108 million live in low and middle income countries.[6] Of those with hearing loss it began in 65 million during childhood.[8] Those who speak sign language and are members of the deaf community see themselves as having a condition rather than illness.[9] Some within this community view cochlear implants with concern as they have the potential to eliminate their culture.[10] The term hearing impairment is often viewed negatively as it emphasis what people cannot do.[9]


Hearing loss exists when there is diminished sensitivity to the sounds normally heard.[8] The terms hearing impairment or hard of hearing are usually reserved for people who have relative insensitivity to sound in the speech frequencies. The severity of a hearing loss is categorized according to the increase in volume above the usual level necessary before the listener can detect it.


Speech perception[edit]

Another aspect of hearing involves the perceived clarity of a sound rather than its amplitude. In humans, that aspect is usually measured by tests of speech perception. These tests measure one's ability to understand speech, not to merely detect sound. There are very rare types of hearing loss which affect speech understanding alone.[11]


The following are some of the major causes of hearing loss.


There is a progressive loss of ability to hear high frequencies with increasing age known as presbycusis. For men, this can start as early as 25 and women at 30, but may even affect teenagers and children. Although genetically variable it is a normal concomitant of aging and is distinct from hearing losses caused by noise exposure, toxins or disease agents.[12]


Noise is the cause of approximately half of all cases of hearing loss, causing some degree of problems in 5% of the population globally.[5] 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.[4]

Populations living near airports or freeways are exposed to levels of noise typically in the 65 to 75 dB(A) range. If lifestyles include significant outdoor or open window conditions, these exposures over time can degrade hearing. The U.S. EPA have set noise standards. The EPA has identified the level of 70 dB(A) for 24‑hour exposure as the level necessary to protect the public from hearing loss and other disruptive effects from noise, such as sleep disturbance, stress-related problems, learning detriment, etc. (EPA, 1974).



Some American health and safety agencies (such as OSHA, the Occupational Safety and Health Administration, and MSHA, the Mine Safety and Health Administration), use an exchange rate of 5 dB.[13] While this exchange rate is simpler to use, it drastically underestimates the damage caused by very loud noise. For example, at 115 dB, a 3 dB exchange rate would limit exposure to about half a minute; the 5 dB exchange rate allows 15 minutes.



Hearing loss has been described as primarily a condition of modern society.[15] In preindustrial times, humans had far less exposure to loud sounds and deafness appears to have been a rare condition.[16] This began to change with the event of machinery and electrical devices in the 18th-20th centuries. Studies have noted that baby boomers most often suffer hearing loss from recreational activities while their parents' generation were more affected by occupational (i.e. workplace) noise.[citation needed] Military service in World War II, the Korean War, and the Vietnam War, has likely also caused hearing loss in large numbers of men from those generations, though proving hearing loss was a direct result of military service is problematic without entry and exit audiograms.[17]



When looking at the genetics of deafness, there are 2 different forms, syndromic and nonsyndromic. Syndromic deafness occurs when there are other medical problems aside from deafness in an individual. This accounts for around 30% of deaf individuals who are deaf from a genetic standpoint.[18] Nonsyndromic deafness occurs when there are no other problems associated with an individual other than deafness. From a genetic standpoint, this accounts for the other 70% of cases, and represents the majority of hereditary hearing loss.[18] Syndromic cases occur with diseases such as Usher syndrome, Stickler syndrome, Waardenburg syndrome, Alport's syndrome, and neurofibromatosis type 2. These are diseases that have deafness as one of the symptoms or as a common feature associated with it. The genetics that correspond with these various diseases are very complicated and are difficult to explain scientifically because the cause is unknown. In nonsyndromic cases where deafness is the only ‘symptom’ seen in the individual it is easier to pinpoint the genes responsible.


  • The most common type of congenital hearing loss in developed countries is DFNB1, also known as Connexin 26 deafness or GJB2-related deafness.
  • The most common recessive syndromic forms of hearing loss are Pendred syndrome, Large vestibular aqueduct syndrome and Usher syndrome.
  • Mutations in PTPRQ are a cause of autosomal-recessive nonsyndromic hearing loss.[20]


  • Measles may cause 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.
  • Presbycusis is a progressive hearing loss accompanying age, typically affecting sensitivity to higher frequencies (above about 2 kHz).
  • Adenoids that do not disappear by adolescence may continue to grow and may obstruct the Eustachian tube, causing conductive hearing loss and nasal infections that can spread to the middle ear.
  • People with HIV/AIDS frequently experience auditory system anomalies.
  • Premature birth causes sensorineural hearing loss approximately 5% of the time.
  • Medulloblastoma and other types of brain tumors can cause hearing loss, whether by the placement of the tumor around the Vestibulocochlear nerve, surgical resection, or platinum-based chemotherapy drugs such as cisplatin.

Neurological disorders[edit]

Neurological disorders such as multiple sclerosis and strokes can have an effect on hearing as well. Multiple sclerosis, or MS, is an autoimmune disease where the immune system attacks the myelin sheath, a covering that protects the nerves. Once the myelin sheaths are destroyed they cannot be repaired. Without the myelin to protect the nerves, nerves become damaged, creating disorientation for the patient. This is a painful process and may end in the debilitation of the affected person until they are paralyzed and have one or more senses gone. One of those may be hearing. If the auditory nerve becomes damaged then the affected person will become completely deaf in one or both ears. There is no cure for MS.[21] Depending on what nerves are damaged from a stroke, one of the side effects can be deafness.[22] Charcot–Marie–Tooth disease variant 1E (CMT1E) is noted for demyelinating in addition to deafness.[23]



Some medications may reversibly affect hearing. This includes some diuretics, aspirin and NSAIDs, and macrolide antibiotics. The link between nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and hearing loss tends to be greater in women, especially those who take ibuprofen six or more times a week.[24] Others may cause permanent hearing loss.[25] On October 18, 2007, the U.S. Food and Drug Administration (FDA) announced that a warning about possible sudden hearing loss would be added to drug labels of PDE5 inhibitors, which are used for erectile dysfunction.[26]


Main article: Ototoxicity

In addition to medications, hearing loss can also result from specific drugs; metals, such as lead; solvents, such as toluene (found in crude oil, gasoline[27] and automobile exhaust,[27] for example); and asphyxiants.[28] Combined with noise, these ototoxic chemicals have an additive effect on a person’s hearing loss.[28]

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.[28] For some ototoxic chemical exposures, particularly styrene,[29] 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.[29] The following list provides an accurate catalogue of ototoxic chemicals:[28][29]

Physical trauma[edit]


People who sustain head injury are especially vulnerable to hearing loss or tinnitus, either temporary or permanent. I. King Jordan lost his hearing after suffering a skull fracture as a result of a motorcycle accident at age 21.[30]


Neurobiological factors[edit]


The process of understanding how sound travels to the brain is imperative in understanding how and why these two reasons would cause a person develops hearing loss. The process is as follows: sound waves are transmitted to the outer ear, sound waves are conducted down to ear canal, bringing the sound waves to the eardrum where they vibrate, these vibrations are now passed through the 3 tiny ear bones in the middle, which cause the fluid to move in the inner ear, the fluid moves the hair cells, the movement of the hair cells cause the vibrations to be converted into nerve impulses, the nerve impulses are taken to the brain by the auditory nerve,[32] the auditory nerve takes the impulses to the medulla oblongata, the brainstem send the impulses to the midbrain, which finally goes to the auditory cortex of the temporal lobe to be interpreted as sound.[33]




The severity of a hearing loss is ranked according to the additional intensity above a nominal threshold that a sound must be before being detected by an individual; it is (measured in decibels of hearing loss, or dB HL). Hearing loss may be ranked as mild, moderate, moderately severe, severe or profound as defined below:

  • Mild:
    • for adults: between 26 and 40 dB HL
    • for children: between 20 and 40 dB HL[8]
  • Moderate: between 41 and 54 dB HL[8]
  • Moderately severe: between 55 and 70 dB HL[8]
  • Severe: between 71 and 90 dB HL[8]
  • Profound: 91 dB HL or greater[8]
  • Totally Deaf: Have no hearing at all.


For certain legal purposes such as insurance claims, hearing loss are described in terms of percentages. Given that hearing loss can vary by frequency and that audiograms are plotted with a logarithmic scale, the idea of a percentage of hearing loss is somewhat arbitrary, but where decibels of loss are converted via a recognized legal formula, it is possible to calculate a standardized "percentage of hearing loss" which is suitable for legal purposes only.



Hearing loss are categorized by their type, their severity, and the age of onset (before or after language is acquired). Furthermore, a hearing loss may exist in only one ear (unilateral) or in both ears (bilateral). There are three main types of hearing loss, conductive hearing loss and sensorineural hearing loss and a combination of the two called mixed hearing loss.[8]

Conductive hearing loss[edit]



Middle ear implants or bone conduction implants can help with this kind of hearing loss.[35]

Sensorineural hearing loss[edit]


Mixed hearing loss[edit]


Before language[edit]

Main article: Prelingual deafness


After language[edit]

Main article: Post-lingual deafness

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.[citation needed] Common treatments include hearing aids, cochlear implants, middle ear implants, bone conduction implants, implants for electric-acoustic stimulation and learning lip reading. 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.

Unilateral and bilateral[edit]


  • hearing conversation on their impaired side
  • localizing sound
  • understanding speech in the presence of background noise.


A similar effect can result from King-Kopetzky syndrome (also known as Auditory disability with normal hearing and obscure auditory dysfunction), which is characterized by an inability to process out background noise in noisy environments despite normal performance on traditional hearing tests.

One reason for the hearing problems these patients often experience is due to the head shadow effect. Newborn children with no hearing on one side but one normal ear could still have problems.[38] Speech development could be delayed and difficulties to concentrate in school are common. More children with unilateral hearing loss have to repeat classes than their peers. Taking part in social activities could be a problem. Early aiding is therefore of utmost importance. Cochlear implants as well as bone conduction implants can help with single sided deafness.[39][40]


The United States Preventive Services Task Force recommends screening for all newborns.[3]

The American Academy of Pediatrics advises that children should have their hearing tested several times throughout their schooling:[14]



It is estimated that half of cases of hearing loss are preventable.[8] A number of preventative strategies are effective including: immunization against rubella to reduce congenital infections, immunization against H. influenza and S. pneumoniae to reduce cases of otitis media, and avoiding or protecting against excessive noise exposure.[8] Education on the perils of hazardous noise exposure increases the use of hearing protectors.[42]



Hearing aids[edit]

Hearing aids are devices that work to improve the hearing and speech comprehension of those with hearing loss.[43] It works by magnifying the sound vibrations in the ear so that one can understand what is being said around them.[43] The use of this technological device may or may not have an effect on one's sociability. Some people feel as if they cannot live without one because they say it is the only thing that keeps them engaged with the public. Others dislike hearing aids very much because they feel wearing them is embarrassing or weird. Due to their low-esteem, they avoid hearing aid usage altogether and would rather remain quiet and to themselves in a social environment.[44]

Cochlear implants[edit]

Illustration of a cochlear implant

Cochlear implants improve outcomes in people with hearing loss in either one or both ears.[45] They work by artificial stimulation of the cochlear nerve by providing an electric impulse substitution for the firing of hair cells. They are expensive, and require programming along with extensive training for effectiveness.

People with cochlear implants are at a higher risk for bacterial meningitis. Thus, meningitis vaccination is recommended.[46] People who have hearing loss, especially those who develop a hearing problem in childhood or old age, may need support and technical adaptations as part of the rehabilitation process. Recent research shows variations in efficacy but some studies[47] 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.

Assistive devices[edit]

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

  • Instant messaging software. In addition, AOL Instant Messenger provides a real-time text feature called Real-Time IM.[50][51]
  • Hearing dogs are a specific type of assistance dog specifically selected and trained to assist the deaf and hearing impaired by alerting their handler to important sounds, such as doorbells, smoke alarms, ringing telephones, or alarm clocks.

Wireless devices[edit]




For a classroom setting, children with hearing loss often benefit from interventions. One simple example is providing favorable seating for the child. Having the student sit as close to the teacher as possible improves the student's ability to hear the teacher's voice and to more easily read the teacher's lips. When lecturing, teachers should try to look at the student as much as possible and limit unnecessary noise in the classroom. In particular, the teacher should avoid talking when their back is turned to the classroom, such as while writing on a whiteboard.

Some other approaches for classroom accommodations include pairing hearing impaired students with hearing students. This allows the hearing impaired student to ask the hearing student questions about concepts that they have not understood. The use of CART (Communication Access Real Time) systems, where an individual types a captioning of what the teacher is saying, is also beneficial.[54] The student views this captioning on their computer. Automated captioning systems are also becoming a popular option.[55] In an automated system, software, instead of a person, is used to generate the captioning. Unlike CART systems, automated systems generally do not require an Internet connection and thus they can be used anywhere and anytime. Another advantage of automated systems over CART is that they are much lower in cost. However, automated systems are generally designed to only transcribe what the teacher is saying and to not transcribe what other students say. An automated system works best for situations where just the teacher is speaking, whereas a CART system will be preferred for situations where there is a lot of classroom discussion.



  no data

Globally hearing loss affects about 10% of the population to some degree.[5] 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).[6] Of these 65 million acquired the condition during childhood.[8] At birth ~3 per 1000 in developed countries and more than 6 per 1000 in developing countries have hearing problems.[8]




Society and culture[edit]

Main article: Deaf culture

Jack Gannon, a professor at Gallaudet University, said this about deaf culture. “Deaf culture is a set of learned behaviors and perceptions that shape the values and norms of deaf people based on their shared or common experiences.” Some doctors believe that being deaf makes a person more social. Dr. Bill Vicar, from ASL University, shared his experiences as a deaf person, "[deaf people] tend to congregate around the kitchen table rather than the living room sofa… our good-byes take nearly forever, and our hellos often consist of serious hugs. When two of us meet for the first time we tend to exchange detailed biographies."[58] Deaf culture is not about contemplating what deaf people cannot do and how to fix their problems, an approach known as the "pathological view of the deaf."[59] Instead deaf people celebrate what they can do. There is a strong sense of unity between deaf people as they share their experiences of suffering through a similar struggle. This celebration creates a unity between even deaf strangers. Dr. Bill Vicars expresses the power of this bond when stating, "if given the chance to become hearing most [deaf people] would choose to remain deaf."[60]

Views of treatments[edit]


Many in the 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 or total communication. Other concerns include loss of deaf culture and limitations on hearing restoration.[10]

The National Association of the Deaf (United States) has a statement on its website regarding cochlear implants.[61] The NAD asserts that the choice to implant is up to the individual (or the parents), yet strongly advocates a fully informed decision in all aspects of a cochlear implant. Much of the negative reaction to cochlear implants stems from the medical viewpoint that deafness is a condition that needs to be "cured," while the Deaf community instead regards deafness a defining cultural characteristic.

Many other assistive devices are more acceptable to the Deaf community, including but not limited to, hearing aids, closed-captioning, email and the internet, text telephones, and video relay services.

Sign language[edit]

Main article: Sign language


Government policies[edit]

Those who are hearing disabled do have access to a free and appropriate public education. If a child does qualify as being hearing impaired and receives an individualized education plan, the IEP team must consider, "the child's language and communication needs. The IEP must include opportunities for direct communication with peers and professionals. It must also include the student’s academic level, and finally must include the students full range of needs"[62] The government also distinguishes between deafness from hearing loss. The U.S. Department of Education states that deafness is hearing loss that is so severe that a person cannot process any type of oral information even if they have some sort of hearing-enhancing device. The U.S. Department of Education states that a hearing loss is when a person's education is affected by how much that person is able to hear. This definition is not included under the term deafness. In order for a person to qualify for special services, they have to hear more than 20 decibels and their educational performance must be affected by their hearing loss. This is what the government has to say about governmental policies and individualized services.

Inclusion vs. pullout[edit]



In a residential school where all the children use the same language (whether it be a school using ASL, Total Communication or Oralism), students will be able to interact normally with other students, without having to worry about being criticized. An argument supporting inclusion, on the other hand, exposes the student to people who aren't just like them, preparing them for adult life. Through interacting, children with hearing disabilities can expose themselves to other cultures which in the future may be beneficial for them when it comes to finding jobs and living on their own in a society where their disability may put them in the minority. These are some reasons why a person may or may not want to put their child in an inclusion classroom.[62]


Sign language: Individuals who experience hearing loss later in life usually do not know sign language.[63]

Driving: Deaf people may use special devices to alert them to sirens or other noises, or panoramic mirrors to enable improved visibility.[64] Many countries allow deaf people to drive, although at least 26 countries do not allow deaf citizens to hold a driver's license.[64]

Hearing aids: While many deaf and hard of hearing individuals do use hearing aids, others may not benefit from the use of a hearing aid.[citation needed]

Deaf Culture: Deaf people may have a variety of different beliefs, experiences, and methods of communication.[63] This may be influenced by the age at which hearing was lost and the individual's personal background.[63]

Telephone usage: People who can't hear can't use a phone. This myth assumes a typical use of a telephone, yet, there are many types of phones. Teletypewriters, video phones, and cell phone text messages are used by deaf people to communicate. A hearing person may use an ordinary telephone and a Telecommunications Relay Service to communicate with a deaf person. Some people with moderate hearing loss may have enough hearing to use amplified telephones, even if they are culturally Deaf and depend primarily on sign language to communicate.[citation needed]

Lip reading: Only about 30% of spoken English is visible on the lips.[63][65] Lip reading requires not only good lighting, but also a good understanding of the oral language in question and may also depend on contextual knowledge about what is being said.[63]

Inheritance: Less than 5% of deaf children in the United States have a deaf parent.[medical citation needed][66]

Communication barriers[edit]


With family[edit]


With peers and in the community[edit]




In the workplace[edit]


To avoid these situations in the workplace, individuals can take full-time or part-time sign language courses. In this way, they can become better able to communicate with the hearing impaired. Such courses teach the American Sign Language (ASL) language as most North Americans use this particular language to communicate. It is a visual language made up of specific gestures (signs), hand shapes, and facial expressions that contain their own unique grammatical rules and sentence structures [69] By completing sign language courses, it ensures that hearing impaired individuals feel a part of the workplace and have the ability to communicate with their co-workers and employer in the manner as other hearing employees do.

In health care[edit]

Not only can communication barriers between deaf and hearing people affect family relationships, work, and school, but they can also have a very significant effect on a deaf individual’s health care. As a result of poor communication between the health care professional and the hearing impaired patient, many patients report that they are not properly informed about their disease and prognosis. [70] This lack of or poor communication could also lead to other issues such as misdiagnosis, poor assessments, mistreatment, and even possibly harm to patients. Poor communication in this setting is often the result of health care providers having the misconception that all people who are hearing impaired have the same type of hearing loss, and require the same type of communication methods. In reality, there are many different types and range of hearing loss, and in order to communicate effectively a health care provider needs to understand that each individual with hearing loss has unique needs. This affects how individuals have been educated to communicate, as some communication methods work better depending on an individual’s severity of hearing loss. For example, assuming every hearing impaired patient knows American Sign Language would be incorrect because there are different types of sign language, each varying in signs and meanings. A patient could have been educated to use cued speech which is entirely different from ASL.[70] Therefore, in order to communicate effectively, a health care provider needs to understand that each individual has unique needs when communicating.





Recent research, reported in 2012 achieved growth of cochlear nerve cells resulting in hearing improvements in gerbils,[75] using stem cells. Also reported in 2013 was regrowth of hair cells in deaf adult mice using a drug intervention resulting in hearing improvement.[76] The Hearing Health Foundation in the US has embarked on an ambitious project called the Hearing Restoration Project.[77] Also Action on Hearing loss in the UK is also aiming to restore hearing.[78]



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External links[edit]