Hearing loss, hearing impairment, or deafness, is a partial or total inability to hear. In children it may affect the development of language and can cause work related difficulties for adults.
It is caused by many factors, including: genetics, aging, exposure to noise, illness, chemicals and physical trauma. Hearing testing may be used to determine the severity of the hearing loss. While the results are expressed in decibels, hearing loss is usually described as mild, mild-moderate, moderate, moderately severe, severe, or profound. Hearing loss is usually acquired by a person who at some point in life had no hearing impairment.
There are a number of measures that can prevent hearing loss and include avoidance of loud noise, chemical agents, and physical trauma. Testing for poor hearing is recommended for all newborns. But, in some cases such as due to disease, illness, or genetics, it is impossible to reverse or prevent. Hearing aids are partially effective for many.
Globally hearing loss affects about 10% of the population to some degree. It caused moderate to severe disability in 124 million people as of 2004 (108 million of whom are in low and middle income countries). Of these 65 million developed the condition during childhood. It is one of the most common medical conditions presenting to physicians. It is viewed by some in the deaf community as a condition, not an illness. Treatments such as cochlear implants have caused controversy in the deaf community.