Hearing loss is the total or partial inability to hear sound in one or both ears. There are many causes of hearing loss – genetic, congenital, infectious, traumatic, toxic, occupational and age-related. They can be divided into two main categories: conductive and sensorineural. Conductive hearing loss (CHL) occurs because of some mechanical problem in the external or middle ear. Sensorineural hearing loss (SNHL) results from a dysfunction of the inner ear. CHL is often reversible, but SNHL is not. People who have both forms of hearing loss are said to have mixed hearing loss.