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Hearing Loss


Lawrence R. Lustig

, MD, Columbia University Medical Center and New York Presbyterian Hospital

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Worldwide, about half a billion people (almost 8% of the world's population) have hearing loss (1). More than 10% of people in the US have some degree of hearing loss that compromises their daily communication, making it the most common sensory disorder. About 1/800 to 1/1000 neonates are born with severe to profound hearing loss. Two to 3 times as many are born with lesser hearing loss. During childhood, another 2 to 3/1000 children acquire moderate to severe hearing loss. Adolescents are at risk from excessive exposure to noise, head trauma, or both. Older adults typically experience a progressive decrease in hearing (presbycusis), which is directly related to a combination of aging, noise exposure, and genetic factors. It is estimated that about 30 million people in the US are exposed to injurious levels of noise on a daily basis.


  • The age at which the hearing loss occurred

  • The nature of the loss (its duration, the frequencies affected, and the degree)



(See also Sudden Hearing Loss.)

General reference

Pathophysiology of Hearing Loss



Sensorineural hearing loss is caused by lesions of either the inner ear (sensory) or the auditory (8th) nerve (neural—see table Differences Between Sensory and Neural Hearing Losses). This distinction is important because sensory hearing loss is sometimes reversible and is seldom life threatening. A neural hearing loss is rarely recoverable and may be due to a potentially life-threatening brain tumor—commonly a cerebellopontine angle tumor. An additional type of sensorineural loss is termed auditory neuropathy spectrum disorder, when sound can be detected but the signal is not sent correctly to the brain, and is thought to be due to an abnormality of the inner hair cells or the neurons that innervate them within the cochlea (1).



Differences Between Sensory and Neural Hearing Losses


Sensory Hearing Loss

Neural Hearing Loss

Speech discrimination

Moderate decrement

Severe decrement

Discrimination with increasing sound intensity



Recruitment in which the perception of sound is exaggerated, especially at high sound levels



Acoustic reflex decay in which the acoustic reflex response is reduced over time during a measurement

Absent or mild


Waveforms in auditory brain stem responses

Well formed with normal latencies for mild to moderate hearing losses; reduced for more severe losses

Absent or with abnormally long latencies

Otoacoustic emissions



Pathophysiology reference

  • 1. Pham NS: The management of pediatric hearing loss caused by auditory neuropathy spectrum disorder. Curr Opin Otolaryngol Head Neck Surg 25(5):396-399, 2017. doi: 10.1097/MOO.0000000000000390

Etiology of Hearing Loss

Hearing loss can be


Congenital Causes of Hearing Loss*

Anatomic Area Affected



External and middle ear


Developmental (eg, ossicular fixation)

Idiopathic (unknown) malformation

Drug-induced malformation (eg, with thalidomide)


Inner ear


Idiopathic (unknown) malformation


Rh incompatibility


Maternal ingestion of ototoxic drugs (eg, for tuberculosis or severe infection)

Drug-induced malformation (eg, with thalidomide)


Central nervous system


Idiopathic (unknown) malformation



* A number of congenital hearing losses may be mixed losses—a combination of conductive and sensory with or without a neural component.

† Causes are listed in approximate order of greatest frequency first.

The most common causes of hearing loss overall are the following:

  • Cerumen accumulation

  • Noise

  • Aging

  • Infections (particularly among children and young adults)


Some Causes of Acquired Hearing Loss


Suggestive Findings

Diagnostic Approach†

External ear (conductive loss)


Visible during examination


Middle ear (conductive loss)

Hearing loss that may fluctuate

Sometimes also dizziness, pain, or fullness in the ear

Usually abnormal-looking TM

Often a history of acute otitis media or other causative event


Audiologic testing with tympanogram

Chronic ear discharge

Usually visible perforation

Granulation tissue or polyp in the canal

Sometimes cholesteatoma


For cholesteatoma, CT or MRI

Apparent by history

Often visible perforation of the TM, blood in the canal or behind the TM (if intact)


Family history

Age at onset in 20s to 30s

Slowly progressive


Tumors (benign and malignant)

Unilateral loss

Often lesion visible during otoscopy


Inner ear (sensory loss)

Genetic disorders (eg, connexin 26 mutation, Waardenburg syndrome, Usher syndrome, Pendred syndrome)

Sometimes a positive family history (but usually negative)


Connexin 26 mutations account for the vast majority of non-syndromic hearing loss cases and should be screened for initially

Sometimes a white forelock of hair or different colored eyes suggests Waardenburg syndrome

Loss of both vision and hearing can suggest Usher syndrome

Genetic testing

CT and/or MRI

Usually apparent by history

Clinical evaluation

> 55 years in men, > 65 years in women

Progressive, bilateral loss

Normal neurologic examination

Clinical evaluation


History of use

Bilateral loss

Variable vestibular symptoms

Renal failure

Clinical evaluation

Blood tests to measure drug levels

Obvious history of infection

Symptoms that begin during or shortly after an infection

Clinical evaluation

Joint inflammation, rash

Sometimes a sudden change in vision or eye irritation

Often known history of the disorder

Serologic testing

Episodes of unilateral, fluctuating hearing loss accompanied by aural fullness, tinnitus, and vertigo

Gadolinium-enhanced MRI to rule out tumor

Barotrauma (with perilymphatic fistula)‡

History of abrupt pressure change (eg, scuba diving, rapid descent in airplane) or a blow to the ear canal

Sometimes severe ear pain or vertigo

Tympanometry and balance function tests

CT of temporal bone

Surgical exploration if vertigo persists

Head trauma (with basilar skull fracture or cochlear concussion)‡

History of significant injury

Possibly vestibular symptoms, facial weakness



Auditory neuropathy‡

Good sound detection, but poor word understanding

Auditory testing (auditory brain stem response [ABR], otoacoustic emissions)


Central nervous system (neural loss)


Unilateral hearing loss, often with tinnitus

Vestibular abnormalities

Sometimes facial or trigeminal nerve deficits

Gadolinium-enhanced MRI

Demyelinating disease (eg, multiple sclerosis)

Unilateral loss


Waxing and waning symptoms

MRI of the brain

Sometimes lumbar puncture

* Each group is listed in approximate order of frequency.

† All patients should have otoscopy and audiologic testing.

‡ Mixed conductive and sensorineural loss may also be present.

TM = tympanic membrane.

Cerumen (earwax) accumulation is the most common cause of treatable conductive hearing loss, especially in older patients. Foreign bodies obstructing the canal are sometimes a problem in children, both because of their presence and because of any damage inadvertently caused during their removal.

Noise can cause sudden or gradual sensorineural hearing loss. In acoustic trauma, hearing loss results from exposure to a single, extreme noise (eg, a nearby gunshot or explosion); some patients develop tinnitus as well. The loss is usually temporary (unless there is also blast damage, which may destroy the tympanic membrane, ossicles, or both). In noise-induced hearing loss, the loss develops over time because of chronic exposure to noise > 85 decibels (dB—see Sound Levels). Even before hearing loss can be documented, noise exposure can damage auditory neurons and their synapses on hair cells; this damage is referred to as "hidden hearing loss" or "synaptopathy," and patients may notice difficulty hearing in noisy environments and have accelerated age-related hearing loss (1). Although people vary somewhat in susceptibility to noise-induced hearing loss, nearly everyone loses some hearing if they are exposed to sufficiently intense noise for an adequate time. Repeated exposure to loud noise ultimately results in loss of hair cells in the organ of Corti. Hearing loss typically occurs first at 4 kHz and gradually spreads to the lower and higher frequencies as exposure continues. In contrast to most other causes of sensorineural hearing losses, noise-induced hearing loss may be less severe at 8 kHz than at 4 kHz.

Aging, together with noise exposure and genetic factors, is a common risk factor for progressive decrease in hearing. Age-related hearing loss is termed presbycusis. Presbycusis is due to a combination of sensory cell (hair cell) and neuronal loss. Research also strongly suggests that early noise exposure accelerates age-related hearing loss. Higher frequencies are more affected than lower frequencies in age-related hearing loss.


Secretory otitis media (SOM) occurs in several ways. Almost all episodes of AOM are followed by a period of 2 to 4 weeks of SOM. SOM can also be caused by eustachian tube dysfunction (eg, resulting from cleft palate, benign or malignant tumors of the nasopharynx, or rapid changes in external air pressure as occur during descent from high altitudes or rapid ascent while scuba diving).


Ototoxic drugs can cause sensorineural hearing loss, and many also have vestibular toxicity.


Sound Levels

Sound intensity and pressure (the physical correlates of loudness) are measured in decibels (dB). A dB is a unitless figure that compares 2 values and is defined as the logarithm of the ratio of a measured value to a reference value, multiplied by a constant:

dB = k log (Vmeasured/Vref)

By convention, the reference value for sound pressure level (SPL) is taken as the quietest 1000-Hz sound detectable by young, healthy human ears.* The sound may be measured in terms of pressure (N/m2) or intensity (watts/m2).

Because sound intensity equals the square of sound pressure, the constant (k) for SPL is 20; for sound intensity, 10. Thus, each 20-dB increase represents a 10-fold increase in SPL but a 100-fold increase in sound intensity.

The dB values in the table below give only a rough idea of the risk of hearing loss. Some of them are dB SPL values (referenced to N/m2), whereas others represent peak dB or dB on the A-scale (a scale that emphasizes the frequencies that are most hazardous to human hearing).




Faintest sound heard by human ear


Whisper, quiet library


Normal conversation, sewing machine, typewriter


Lawnmower, shop tools, truck traffic (90 dB for 8 hours a day is the maximum exposure without protection†)


Chain saw, pneumatic drill, snowmobile (2 hours a day is the maximum exposure without protection)


Sandblasting, loud rock concert, automobile horn (15 minutes a day is the maximum exposure without protection)


Gun muzzle blast, jet engine (noise causes pain and even brief exposure injures unprotected ears; injury may occur even with hearing protectors)


Rocket launching pad

* In audiometric testing, because human ears respond differently at different frequencies, the reference value changes for each frequency tested. Threshold values reported on audiograms take this into account; the normal threshold is always 0 dB, regardless of the actual sound pressure level (SPL).

† This is the mandatory federal standard, but protection is recommended for more than brief exposure to sound levels > 85 dB.

Etiology reference

  • 1. Liberman MC, Kujawa SG: Cochlear synaptopathy in acquired sensorineural hearing loss: manifestations and mechanisms. Hear Res 349:138-147, 2017. doi: 10.1016/j.heares.2017.01.003

Evaluation of Hearing Loss



Most adults and older children notice a sudden hearing loss, and caregivers may suspect that a neonate has a severe hearing loss within the first weeks of life when the neonate does not respond to voices or other sounds. However, progressive losses and nearly all losses in infants and young children must be detected by screening. Screening in children should begin at birth so that linguistic input can allow optimal language development. If screening is not done, severe bilateral losses may not be recognized until age 2 years, and mild to moderate bilateral or severe unilateral losses are often not recognized until children reach school age.

Screening in older people should be considered because patients may not have noticed a gradual decline in hearing or may think it a normal consequence of aging.



History of present illness should note how long hearing loss has been perceived, how it began (eg, gradual, acute), whether it is unilateral or bilateral, and whether sound is distorted (eg, music is off—dull or lifeless) or there is difficulty with speech discrimination. The patient should be asked whether the loss followed any acute event (eg, head injury, loud noise exposure, barotrauma [particularly a diving injury], or starting of a drug). Important accompanying symptoms include other otologic symptoms (eg, ear pain, tinnitus, ear discharge), vestibular symptoms (eg, disorientation in the dark, vertigo), and other neurologic symptoms (eg, headache, weakness or asymmetry of the face, an abnormal sense of taste, fullness of the ear). In children, important associated symptoms include presence of delays in speech or language development, visual changes, or delayed motor development.


Past medical history should note previous possibly causative disorders, including central nervous system infection, repeated ear infections, chronic exposure to loud noise, head trauma, rheumatic disorders (eg, rheumatoid arthritis, lupus), and a family history of hearing loss. Drug history should specifically query current or previous use of ototoxic drugs. For young children, a birth history should be sought to determine if there were any intrauterine infections or birth complications.

Physical examination

The focus is examination of the ears and hearing and the neurologic examination. The external ear is inspected for obstruction, infection, congenital malformations, and other lesions. The tympanic membrane (TM) is examined for perforation, drainage, otitis media (pus or fluid seen in the middle ear through the TM), and cholesteatoma. During the neurologic examination, particular attention needs to be paid to the 2nd through 7th cranial nerves as well as to vestibular and cerebellar function because abnormalities in these areas often occur with tumors of the brain stem and cerebellopontine angle. The Weber and Rinne tests require a tuning fork to differentiate conductive from sensorineural hearing loss.



Red flags

Findings of particular concern are

  • Unilateral sensorineural hearing loss

  • Abnormalities of cranial nerves (other than hearing loss)

  • Rapidly worsening or sudden hearing loss

Interpretation of findings

Many causes of hearing loss (eg, cerumen, injury, significant noise exposure, infectious sequelae, drugs) are readily apparent based on results of the history and examination (see table Some Causes of Acquired Hearing Loss).

Associated findings are helpful in diagnosing the remaining small number of patients in whom no clear cause can be found. Patients who have focal neurologic abnormalities are of particular concern. The 5th or 7th cranial nerve or both are often affected by tumors that involve the 8th nerve, so loss of facial sensation and weak jaw clench (5th) and hemifacial weakness and taste abnormalities (7th) point to a lesion in that area. Signs of autoimmune disorders (eg, joint swelling or pain, eye inflammation) or renal dysfunction may suggest these disorders as a cause. Maxillofacial malformations may suggest a genetic or developmental abnormality.



Testing includes

  • Audiologic tests

  • Sometimes MRI or CT


  • Measurement of pure-tone thresholds with air and bone conduction

  • Speech reception threshold

  • Speech discrimination

  • Tympanometry

  • Acoustic reflex testing



Speech audiometry includes the speech reception threshold (SRT) and the word recognition score. The SRT is a measure of the intensity at which speech is recognized. To determine the SRT, the examiner presents the patient with a list of words at specific sound intensities. These words usually have 2 equally accented syllables (spondees), such as "railroad," "staircase," and "baseball." The examiner notes the intensity at which the patient repeats 50% of the words correctly. The SRT approximates the average hearing level at speech frequencies (eg, 500 Hz, 1000 Hz, 2000 Hz).



The acoustic reflex is contraction of the stapedius muscle in response to loud sounds, which changes the compliance of the TM, protecting the middle ear from acoustic trauma. The reflex is tested by presenting a tone and measuring what intensity provokes a change in middle ear impedance as noted by movement of the TM. An absent reflex could indicate middle ear disease or a tumor of the auditory nerve. Any conductive hearing loss abolishes the acoustic reflex. Additionally, facial paralysis abolishes the reflex because the facial nerve innervates the stapedius muscle.

Audiogram of right ear in a patient with normal hearing


Normal thresholds are 0 dB +/ 10 dB. Patients with a hearing threshold below 20 dB are considered to have average or better-than-average hearing. The greater the dB, the louder is the sound and the worse the hearing.

"O" is the standard symbol for air conduction of the right ear; "X" is the standard symbol for air conduction for the left ear. The "<" is the standard symbol for unmasked bone conduction for the right ear; ">" is the standard symbol for unmasked bone conduction of the left ear.

The reason why both masked and unmasked measures are needed is to make sure one ear is not hearing the sound presented to the other ear (one ear is 'masked' so it does not hear the sound presented to the other ear, giving a false value).

Audiogram of right ear in a patient with normal hearing


CT is done if bony tumors or bony erosion is suspected. Magnetic resonance angiography and venography is done if vascular abnormalities such as glomus tumors are suspected.



Otoacoustic emissions testing measures sounds produced by outer hair cells of the cochlea in response to a sound stimulus usually placed in the ear canal. These emissions are essentially low-intensity echoes that occur with cochlear outer hair cell activation. Emissions are used to screen neonates and infants for hearing loss and to monitor the hearing of patients who are using ototoxic drugs (eg, gentamicin, cisplatin).

Central auditory evaluation measures discrimination of degraded or distorted speech, discrimination in the presence of a competing message in the opposite ear, the ability to fuse incomplete or partial messages delivered to each ear into a meaningful message, and the capacity to localize sound in space when acoustic stimuli are delivered simultaneously to both ears. This testing should be done on certain patients, such as children with a reading or other learning problem and older people who seem to hear but do not comprehend.

In children with hearing loss, additional testing should include an ophthalmologic examination because many genetic causes of deafness also cause ocular abnormalities. Children with unexplained hearing loss should also have an ECG to look for long QT syndrome and possibly also genetic testing.

Treatment of Hearing Loss

The causes of a hearing loss should be determined and treated. Ototoxic drugs should be stopped or the dose should be lowered unless the severity of the disease being treated (usually cancer or a severe infection) requires that the risk of additional ototoxic hearing loss be accepted. Attention to peak and trough drug levels is mandatory to help minimize risk and should be obtained in all patients. In patients with renal dysfunction, adjustments to drug dosages with close attention to peak and trough levels are required to minimize the risk of ototoxicity (eg, see dosing considerations for aminoglycoside antibiotics). There are some genetic abnormalities involving the mitochondria that increase the sensitivity to aminoglycoside antibiotics, and these can be identified with genetic screening.

Fluid from middle ear effusion can be drained by myringotomy and prevented from reaccumulating with the insertion of a tympanostomy tube. Benign growths (eg, enlarged adenoids, nasal polyps) and malignant tumors (eg, nasopharyngeal cancers, sinus cancers) blocking the eustachian tube or ear canal can be removed. Hearing loss caused by autoimmune disorders may respond to corticosteroids.

Damage to the tympanic membrane or ossicles or otosclerosis may require reconstructive surgery. Brain tumors causing hearing loss may in some cases be removed or radiated and hearing preserved.


Hearing aids



The best models are adjusted to a person’s particular pattern of hearing loss. For example, people with mainly high-frequency hearing loss might not benefit from simple amplification, which merely makes the garbled speech they hear sound louder; they usually need a hearing aid that selectively amplifies the high frequencies. Some hearing aids contain vents in the ear mold, which facilitate the passage of high-frequency sound waves. Some use digital sound processing with multiple frequency channels so that amplification more precisely matches hearing loss as measured on the audiogram.






Cochlear implants

Patients with advanced levels of hearing loss, including those with some residual (natural) hearing but who even with a hearing aid cannot understand more than half of the words contained in connected speech, may benefit from a cochlear implant. The surgery may result in loss of some residual hearing. However, even if residual hearing is lost, cochlear implants can greatly improve hearing, even in people who are profoundly deaf.



Outcomes with cochlear implants vary, depending on a number of factors, including the

  • Length of time between onset of hearing loss and placement of the implant (shorter duration leads to better outcomes)

  • Cause of the underlying hearing loss

  • Position of the implant within the cochlea

Brain stem implants

Although cochlear implants are not an option for patients who have had both acoustic nerves destroyed (eg, by bilateral temporal bone fractures or neurofibromatosis) or are born without cochlear nerves, these patients can have some hearing restored by means of brain stem implants that have electrodes connected to sound-detecting and sound-processing devices similar to those used for cochlear implants, although usually not as good. In general, children born without cochlear nerves who receive the brain stem implant tend to have more hearing restored than patients who receive it following vestibular neuroma resection. Results of the brain stem implant range from assistance with lip-reading skills to the ability to understand language without lip-reading (termed 'open-set speech' understanding).

Assistive strategies and technologies




People with profound hearing loss often communicate by using sign language. American Sign Language (ASL) is the most common version in the US. Other forms of linguistic communication that utilize visual inputs include Signed English, Signing Exact English, and Cued Speech. Around the world, it has been estimated that there are over 300 unique sign languages, with different countries, cultures, and villages having their own unique form of sign language.

Single-Sided Deafness

Patients with single-sided deafness (SSD) represent a special challenge. In one-on-one situations, hearing and speech understanding is relatively unaffected. However, with noisy backgrounds or complex acoustic environments (eg, classrooms, parties, meetings), patients with SSD are unable to hear and communicate effectively. Further, patients who hear out of only one ear are unable to localize the origin of sounds. The "head shadow" effect is the skull's ability to block sound coming from the deaf side from reaching the hearing ear. This can result in up to a 30 dB loss of sound energy reaching the hearing ear (as a comparison, a store-bought ear plug results in a 22 to 32 dB drop in hearing, roughly equivalent). For many patients, SSD can be life-altering and lead to significant disability at work and socially.

Treatment for SSD includes contralateral routing of signal (CROS) hearing aids or bone-anchored hearing implants that pick up sound from the deaf side and transfer it to the hearing ear without the loss of sound energy. Although these technologies improve hearing in noisy settings, they do not allow sound localization. Cochlear implants are increasingly being used with success in patients with SSD, particularly if the deaf ear also has severe tinnitus; implants have also been shown to provide sound localization.

Treatment of Hearing Loss in Children


If infants as young as 1 month have profound bilateral hearing loss and cannot benefit from hearing aids, they can be candidates for a cochlear implant. Although cochlear implants allow auditory communication in many children with either congenital or acquired deafness, they are generally more effective in children who already have developed language. Children who have postmeningitic deafness eventually develop an ossified inner ear that prevents the placement of an implant; they should receive cochlear implants as soon as possible to allow the implant to be correctly placed and maximize effectiveness. Children whose acoustic nerves have been destroyed by tumors may be helped by implantation of brain stem auditory-stimulating electrodes. Children with cochlear implants may have a slightly greater risk of meningitis than children without cochlear implants or adults with cochlear implants.


Prevention of Hearing Loss

Prevention of hearing loss consists mainly of limiting duration and intensity of noise exposure. People required to expose themselves to loud noise must wear ear protectors (eg, plastic plugs in the ear canals or glycerin-filled muffs over the ears). The Occupational Safety and Health Administration (OSHA) of the US Department of Labor and similar agencies in many other countries have standards regarding the length of time that a person can be exposed to a noise (see OSHA's occupational noise exposure standards). The louder the noise, the shorter the permissible time of exposure.

Geriatrics Essentials

Older people typically experience a progressive decrease in hearing (presbycusis). In the United States, 40% of those who are hearing impaired are older. Hearing impairment is prevalent in over one third of people over age 65 years and over half of people over age 75 years, making it the most common sensory disorder in this population. Nonetheless, hearing loss in older people should be evaluated and not ascribed simply to aging; older patients may have a tumor, a neurologic or autoimmune disorder, or an easily correctable conductive hearing loss. Also, recent research strongly suggests that hearing loss in older people can facilitate dementia, which may be mitigated by properly correcting hearing loss.





A screening tool is often helpful for older people because many do not complain of hearing loss. One tool is the Hearing Handicap Inventory for the Elderly–Screening Version, which asks



  • Do you have difficulty hearing when someone whispers?

  • Do you feel handicapped by a hearing problem?








Key Points about Hearing Loss


  • All patients with hearing loss should have audiologic testing.


More Information about Hearing Loss


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