We hear sounds when sound energy goes through the ear's three main structures . In hearing loss, one or more of these structures is damaged. These structures are the:

• External ear canal.
• Middle ear, which is separated from the ear canal by the eardrum.
• Inner ear, which contains the cochlea, the main sensory organ of hearing.

Which part of the ear is affected determines the type of hearing loss.

• In conductive hearing loss, sound energy is blocked before it reaches the inner ear. Examples of conductive hearing loss include earwax or a growth blocking sound, such as occurs in otosclerosis.
• In sensorineural hearing loss, sound reaches the inner ear, but a problem in the inner ear or the nerves that allow you to hear (auditory nerves) prevent proper hearing. Examples of sensorineural hearing loss include both noise-induced and age-related hearing loss.

A mixed hearing loss, in which both the conductive and sensorineural systems are affected, can also occur.

Another type of hearing loss is central hearing loss. In this type of hearing loss, the ear works, but the brain has trouble understanding sounds because the parts that control hearing are damaged. It may occur after a head injury or stroke. This type of hearing loss is rare.

Undiagnosed and untreated hearing loss can contribute to depression, social isolation, and loss of independence, especially in older adults.