As adults age, they can develop hearing loss, which can be partial (hearing impairment) or complete (deafness). Conductive hearing loss is caused by obstruction of or mechanical damage to the outer or middle ear. Sensorineural hearing loss is usually permanent and is caused by damage to the auditory nerve (a nerve that relays hearing information to the brain) or the inner ear. Presbycusis refers to age- associated sensorineural hearing loss and is the most common cause of hearing loss in older adults. In 2008, 31% of Americans older than 65 years had presbycusis and 70% older than 85 years had presbycusis. Risk factors for hearing loss include chronic exposure to loud machinery or music, chronic ear infections, increasing age, and genetic predisposition (passed on from parents to children).