Deafness: Deafness is defined by partial or complete hearing loss. Levels of hearing impairment vary from a mild but important loss of sensitivity to a total loss of hearing. Older adults suffer most often from hearing loss. Age-related hearing loss affects 30 to 35 percent of the population between the ages of 65 and 75 years, and 40 percent of the population over the age of 75. The most common cause of hearing loss in children is otitis media, a disorder that affects predominantly infants and young children. A substantial number of hearing impairments are caused by environmental factors such as noise, drugs, and toxins. Many sensorineural hearing losses result from a genetic predisposition.