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Hearing impairment

Hearing impairment, or deafness, is when your hearing is affected by a disease, disorder or injury.

The ear consists of three parts: the outer ear, the middle ear and the inner ear. The outer ear is made up of the visible part of the ear on the side of your head, the ear canals that go into your head and the eardrum. The eardrum is a thin layer of tissue that separates the outer ear from the middle ear.

Sound waves entering your ear make the eardrum vibrate. These vibrations pass on to the three small bones, called ossicles, that make up the middle ear. The ossicles amplify the vibrations and pass them on to your inner ear.

The inner ear is made up of the cochlea and the auditory nerve. The cochlea contains tiny cells, called hair cells, that move in response to the vibrations passed from the middle ear. The movement of the hair cells generates an electrical signal that is transmitted to your brain through the auditory nerve.

Doctors divide hearing impairment into two types: conductive hearing loss and sensorineural hearing loss. Conductive hearing loss is caused when something interferes with the transmission of sound from your outer ear to the inner ear. Sensorineural hearing loss is caused when there is a problem with your inner ear, or the pathway from the inner ear to your brain.

There are different levels of hearing impairment, defined by the quietest sound you hear, measured in decibels:

  • Mild deafness If you have mild deafness the quietest sounds you can hear are between 25 and 39 decibels. Mild deafness can cause some difficulty following speech, in noisy areas.
  • Moderate deafness If you have moderate deafness the quietest sounds you can hear are between 40 and 69 decibels. People with moderate deafness may have difficulty following speech without a hearing aid.
  • Severe deafness If you have severe deafness the quietest sounds you can hear are between 70 and 94 decibels. People with severe deafness will usually need to rely on lip-reading or sign language, even with a hearing aid.
  • Profound deafness If you have profound deafness the quietest sounds you can hear are 95 decibels or more. People with profound deafness will usually need to rely on lip-reading or sign language.

Hearing loss can be present at birth or develop in childhood or adulthood. People who are born able to hear but who become severely or profoundly deaf after learning to speak are sometimes described as deafened.

The leading charity for deaf and hearing impaired people, the RNID, estimates that there are almost nine million deaf and hearing impaired people in the UK. This number is expected to rise as the number of people over the age of 60 increases.

Reproduced under the terms of Click-Use Licence number C2009000382. The content of this page has been published under a Click-Use Licence (link this to http://www.opsi.gov.uk/click-use/index) which covers the use of core Crown copyright information. The original material can be found on NHS Choices.