Otosclerosis is a condition that can cause deafness. In a patient with otosclerosis, instead of the small bones of the inner ear touching each other, there is a growth of spongy tissue between them. As this tissue is not rigid, the vibrations are not carried as well to the cochlea, and hearing is affected. Even if the tissue later hardens, the inner ear loses its function.

Otosclerosis is a chronic condition that develops gradually, causing progressive loss of hearing, sometimes until the sufferer is functionally deaf. It is usually detected in the teenage years, or the twenties. Diagnosis may be later if the growth does not at first affect the hearing. Hearing loss alomst always follows a typical pattern. First the high frequencies are lost, then the low frequencies, and finally the middle frequencies. Other symptoms include tinnatus, and problems with balance.

Otosclerosis is more common in women than men, and pregnancy usually increases its effect. It is caused by a gene that is dominant, but does not always cause the condition when present.