Otosclerosis involves the formation of new bone that affects two structures within the ear, known as the cochlea and labyrinth. The cochlea is a cone-shaped tube involved in hearing, and the labyrinth is key to a person's sense of balance.

What is going on in the body?

When new bone forms over the inner ear structures, it can prevent the bones from vibrating normally. The bones are no longer able to transmit sound waves to the cochlea, and hearing is impaired. If the labyrinth is affected, the person's sense of balance can be impaired as well.

What are the causes and risks of the condition?

Many cases have no known cause. In others, there is a clear family history. Osteogenesis imperfecta, a genetic disease that causes bones to be brittle, often leads to otosclerosis. There is some thought that drinking non-fluoridated water may cause a susceptible person to develop otosclerosis as well.