Noise -- sound is picked up by a small, spiral-shaped organ called the cochlea that is located within the inner ear. Thousands of tiny hairs in the cochlea sense the vibration and pass the message to the brain via the cochlear nerve. These sensitive hairs can be damaged by excessive noise. The scar tissue that results from this damage can't conduct sound. Ringing in the ears (tinnitus) after exposure to loud noise is a warning sign that your ears have been overloaded.
Drugs -- certain chemicals and drugs can damage your hearing if taken over long periods of time.
Disease -- some diseases, such as measles, mumps, rubella (German measles) and meningitis, can cause loss of hearing.
Injury -- including perforation of the ear drum, fractured skull or large changes in air pressure (barotrauma).