Hearing loss, also known as hearing impairment, is a sudden or gradual decrease in the ability to hear. Although hearing loss is especially common in older adults, it affects people of all ages, can range from mild to severe, and can be reversible, temporary, or permanent.

The most common causes of hearing loss are age and exposure to noise over a long period of time. People who have hearing loss are sometimes not aware of it, especially when the loss has developed gradually. Some people are born without hearing (congenital hearing loss).

Hearing loss can be conductive or sensorineural.

• In conductive hearing loss, the transmission of sound (conduction) is misdirected or blocked from passing into the inner ear. Anything that disrupts the passage of sound through the external and middle ear—such as hardened earwax, a foreign object, abnormal bone growth, swelling, or a tumor—can cause this type of hearing loss. Conductive hearing loss usually can be reversed by treating the cause.
• In sensorineural hearing loss, sound reaches the inner ear, but a problem in the inner ear—or in the cochlear (auditory) nerve or, in rare cases, in the brain itself—prevents proper hearing. Damage to the tiny hair cells in the cochlea, resulting from age-related changes or repeated noise exposure, is the most common cause of sensorineural hearing loss. Conditions such as stroke, multiple sclerosis, or a tumor sometimes cause nerve damage that may result in sensorineural hearing loss.

Hearing loss is sometimes reversible. If it is not, hearing aids and other devices can help the person adapt to reduced hearing and help make communication, social interaction, and work and leisure activities easier and more enjoyable.