In the inner ear, the delicate nerve mechanisms which convert mechanical energy (the movement of the fluid in the cochlea) into nerve impulses can be easily and permanently damaged in a variety of ways.

The result of hearing loss to the inner ear and its connecting nerves is referred to as a sensorineural hearing impairment.

It is also frequently referred to as a "nerve deafness" often, but not always, an accurate description.

Sensorineural hearing losses are considerably more serious then conductive losses because they usually involve a higher degree of impairment and are not as easily corrected. Hearing problems caused by inner ear damage are usually not medically or surgically treatable. For most sensorineural impairments (about 90% of the hearing impaired), the only effective solutions and hearing aids, sometimes supplemented by auditory training and lip reading. At times both conductive and sensorineural deafness exist, called mixed hearing impairment.

Some drugs and antibiotics can alter function of the hair cell or damage the auditory nerve. Several congenital conditions produce one or the other type of hearing loss, or a mixture. Hereditary, tumors, traumatic injury, and hearing loss associated with aging are mainly sensorineural.

Hearing loss due to advancing age is the most common cause. This is called presbycusis, and is identified as a gradual decline in hearing ability, especially for high-pitched sounds, and become worse with age.

Unfortunately our ears do not escape the changes that occur throughout the body as we grow older. It is not due to age per se, but due to the continuous assault of sound on our ears over time which actually kills off some of the hairlike cells of the cochlea and possibly damages the auditory nerve. When cochlear damage occurs, the hairs often die in cluster: a cluster receiving vibrations for one particular pitch of sound may be affected before clusters of hair cells for other pitches. Particularly susceptible are those clusters handling the higher tones, which explains the difficulty hearing voices of women and children.

Although the hearing loss is primarily thought to affect the cochlea, persons with presbycusis can also show auditory problems within the auditory nerve and auditory pathway to the brain as well.

Hearing loss due to noise exposure is also common and is difficult to distinguish from hearing loss doe to advancing age.

In some cases the noise damage is due to single, very loud impact type noise (explosion). In this case the loss is immediate and usually incurable. In other cases the hearing loss is due to less intense, but continuous loud sounds (machinery, etc). The loss is gradual over time and since there is no pain, may pass unnoticed at first. Sometimes the extent of damage is greatest to the ear which receives the greatest exposure (i.e. sport rifles and shotguns, truck drivers with window open).

Drugs and medications, such as quinine, some antibiotics, and even aspirin, can cause hearing loss.
The category of antibiotics called aminoglycosides (gentamicin, neomycin, streptomycin and several others) are ototoxic,or harmful to the ear, in 1% to 75% of patients, depending on dosage and how long treatment lasts. These drugs destroy hair cells.

Those who already have noise-induced hearing loss are especially vulnerable, as are the elderly and those with kidney failure (who for unknown reasons have an unusually high incidence of hearing loss even without drug use)

The use of diuretics increases the likelihood that aminoglycosides will damage hearing.
Aspirin, when taken in large doses, has been known to cause hearing impairment which can return to pre-medication levels after the medication is discontinued.
Certain drugs taken for cancer treatment may also lead to hearing impairment which is permanent in nature, with the loss being worse with greater dosages.
Meniere's syndrome is characterized by head noises, nausea, fullness of ear, dizziness and fluctuating hearing loss in one ear. Thought to be caused by increased fluid pressure in cochlea, this condition may sometimes be alleviated by medical and/or surgical treatment, but the hearing is not restored.
A reduced blood supply to the inner ear or injuries to the head may damage the inner ear structure.
Illness accompanied with high fever, especially for a prolonged time.
Other causes, such as meningitis, benign growths situated in the hearing nerve, and viral infections (mumps and measles) can cause hearing impairments. Others are related more specifically to children.

Approximately 10% of all hearing losses can be helped medically or by surgery. Most of the rest require hearing aids.

Central Hearing Disorders

Sometimes, the ability to hear is impaired along the auditory pathways that lead to the brain or in the auditory centers within the brain itself. The centers responsible for decoding signals that represent sounds can be damaged by head trauma, strokes, tumors, or genetic defects, among other things. People so affected do not necessarily have a hearing loss, but cannot fully use what they hear. Deficits in attention span, delays in the ability to process information, or impaired memory may accompany such a condition.

In this setting, if the rest of the auditory apparatus is normal, hearing aids can still be of assistance, but not to the same degree as if the loss were limited to the inner ear and its associated structures. Complex hearing rehabilitation is required.

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