In India Otosclerosis is one of the commonest causes of deafness with an intact ear drum. When sound waves fall upon the ear drum, it vibrates. These vibrations are transmitted by a chain of 3 mobile bones called ossicles in the middle ear from the drum to the inner ear.

Otosclerosis is a microscopic abnormal growth of bone in the walls of the inner ear. This abnormal growth causes the stapes bone (also called the "stirrup") to become immobile or "fixed". Normally the stapes vibrates freely to allow the transmission of sound to the inner ear, but when it cannot move, it prevents sound waves from reaching the inner
ear fluids, and hearing is impaired.

Otosclerotic bone sometimes involves other structures of the inner ear, thereby affecting the nerves of the inner ear. When this occurs it also causes a distortion or difficulty in understanding the speech of others, regardless of how loudly they talk.

Otosclerosis affects only the ears and involves both ears usually one after another. It occurs in both men and women but women are usually affected slightly more frequently. This is a disease of the early middle age and thus affects people in the prime of life. Pregnancy is known to aggravate the situation. Otosclerosis tends to be familial, but there is no pattern to its heredity.