In adults, the most common causes of hearing loss are:

• Noise. Noise-induced hearing loss can affect people of all ages and most often develops gradually over many years. Over time, the noise experienced at work, during recreation (such as riding motorcycles), or even common chores (such as using a power lawn mower) can lead to hearing loss.
• Age. In age-related hearing loss (presbycusis), changes in the nerves and cells of the inner ear that occur as you get older cause a gradual but steady hearing loss. The loss may be mild or severe, but it is always permanent.

Other causes of hearing loss include:

• Earwax buildup or an object in the ear. Hearing loss because of earwax is common and easily treated.
• Ototoxic medicines (such as certain antibiotics) and other substances (such as arsenic, mercury, tin, lead, and manganese) that can damage the ear.
• Injury to the ear or head. Head injuries can also damage the structures in the ear and cause a sudden hearing loss.
• Ear infection, such as a middle ear infection (otitis media) or an infection of the ear canal (otitis externa or swimmer's ear).
• Fluid in the middle ear after a cold or the flu, or after traveling on an airplane.
• Otosclerosis, a condition that affects the bones of the middle ear.
• Acoustic neuroma, a noncancerous tumor on the nerve that helps people hear.
• Ménière's disease. Ménière's disease may result in temporary or permanent hearing loss.
• Noncancerous (benign) growths in the ear canal, such as exostoses, osteomas, and glomus tumors. Exostoses are bone growths that often develop when the ear canal is repeatedly exposed to cold water or cold air. Osteomas and glomus tumors are noncancerous tumors. These all can cause hearing loss if they block the ear canal. A glomus tumor that occurs elsewhere in the head can also affect hearing.

Other medical conditions that do not affect the ear directly may also cause hearing loss.

• An interruption of the blood flow to the inner ear or parts of the brain that control hearing may lead to hearing loss. This may be caused by heart disease, stroke, high blood pressure, or diabetes.
• Autoimmune hearing loss can occur in one or both ears and can come and go or get worse over 3 to 4 months. An autoimmune disease, such as rheumatoid arthritis, may be present.

What happens in hearing loss?

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. More than 90% of hearing loss is sensorineural, and of this group, age-related hearing loss is the most common.²