Hearing loss is any degree of impairment of the ability to understand sound. A drop of more than 10 decibels (a unit measuring the loudness of sound) in what a person can hear is significant.

Hearing can be interrupted at many stages as sound waves pass through the air of the external ear, the bones of the middle ear, and the liquid of the inner ear. Hearing loss can also occur as hearing-related impulses are transmitted along the nerves to the brain, or within the brain, where the impulses may be misinterpreted.

The external ear canal can be blocked by ear wax, foreign objects, infection, and tumors. Overgrowth of bone, which occurs when the ear canal has been flushed with cold water repeatedly for years, can also narrow the passageway, making blockage and infection more likely. This condition occurs often in Northern California surfers and is therefore...