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Causes
By Mayo Clinic staff
How you hear
Hearing occurs when sound waves reach the structures inside your ear, where the sound wave vibrations are converted into nerve signals that your brain recognizes as sound.
Your ear consists of three major areas: the outer ear, middle ear and inner ear. Sound waves pass through the outer ear and cause vibrations at the eardrum. The eardrum and three small bones of the middle ear — the hammer, anvil and stirrup — amplify the vibrations as they travel to the inner ear. There, the vibrations pass through fluid in the cochlea, a snail-shaped structure in the inner ear.
Attached to nerve cells in the cochlea are thousands of tiny hairs that help translate sound vibrations into electrical signals that are transmitted to your brain. The vibrations of different sounds affect these tiny hairs in different ways, causing the nerve cells to send different signals to your brain. That's how you distinguish one sound from another.
What causes hearing loss
For some people, the cause of hearing loss is the result of a gradual buildup of earwax, which blocks the ear canal and prevents conduction of sound waves. Earwax blockage is a cause of hearing loss among people of all ages.
In most cases, however, hearing loss results from damage to the inner ear. Aging and prolonged exposure to loud noise may cause wear and tear on the hairs or nerve cells in the cochlea that send sound signals to the brain. When these hairs or nerve cells are damaged or missing, electrical signals aren't transmitted as efficiently, and hearing loss occurs. Higher pitched tones may become muffled to you. It may become difficult for you to pick out words against background noise. Heredity may make you more prone to these changes.
Ear infection and abnormal bone growths or tumors of the outer or middle ear can cause hearing loss. A ruptured eardrum also may result in loss of hearing.
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- Common sounds. National Institute on Deafness and Other Communication Disorders. http://www.nidcd.nih.gov/health/education/teachers/common_sounds.asp. Accessed June 26, 2009.
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- How loud is too loud? American Tinnitus Association. http://www.ata.org/about-tinnitus/how-loud-too-loud. Accessed July 15, 2009.
