What is deafness? Deafness means difficulty hearing noise. It can be mild, moderate, severe or profound. for example, people with mild deafness have some difficulty following speech, mainly in noisy situations. Those with moderate deafness have difficulty following speech without a hearing aid. People who are severely deaf rely a lot on lip-reading, even with a hearing aid. British Sign Language (BSL) may be their first or preferred language. Profoundly deaf people need to lip-read to understand speech.

BSL may be their first or preferred language. Deafness can cause difficulty communicating and people who are deaf may be at risk of physical and social isolation. They are also at greater risk of accidents because they may not hear warning alarms and sirens. In the UK, there are an estimated 9 million deaf and partially hearing people. About 688,000 of these are severely or profoundly deaf. Babies' hearing is tested as part of routine screening. About 840 babies are born with significant deafness each year in the UK. About one in 1,000 children is deaf at three years old and about 20,000 children aged up to 15 are moderately to profoundly deaf. But the commonest cause of hearing loss is ageing, and three-quarters of people who are deaf are aged over 60. From 40 years old, more men than women become hard of hearing. Among people over the age of 80, more women than men are deaf or hard of hearing, not because women are more likely to become deaf but because they live longer and there are more of them.

How does the ear work?: The external parts of our ear act like trumpets to collect sound and funnel it into the external ear canal. The pressure waves that form sound hit the ear-drum at the end of the ear canal and are then transmitted across a chamber known as the middle ear, to the sensory organs of the inner ear. An organ known as the cochlea, deep within the inner ear in the skull, is responsible for converting the mechanical vibration of sound into electrical signals. These can then be detected by the brain.

What causes hearing loss? It can result from damage or disruption to any part of the hearing system. Causes can range from wax blocking the ear canal and age-related changes to the sensory cells of the cochlea to brain damage. Common causes of deafness in adults include presbyacusis (age-related hearing loss due to deterioration of the inner ear), side-effects of medication, acoustic neuroma (a tumour of the nerve which carries hearing signals) and Meniere's disease. Common causes of deafness in children include inherited conditions, infection during pregnancy, meningitis, head injury and glue ear (more correctly known as otitis media, where fluid builds up in the middle ear chamber and interferes with the passage of sound vibrations, generally as a result of viral or bacterial infection). Common temporary causes include earwax, infection, glue ear and foreign body obstruction.

Noise and hearing loss: Excessive exposure to noise is an important cause of a particular pattern of hearing loss, contributing to problems for up to 50 per cent of deaf people. Often people fail to realise the damage they're doing to their ears until it's too late. Although loud music is often blamed (and MP3 players are said to be storing up an epidemic of deafness in years to come) research has also blamed tractors (for deafness in children of farmers), aircraft noise, sports shooting and even cordless telephones.

Treatment: Many different tactics can help to reduce the risk of hearing loss, and to help those who do develop problems. Vaccination against infections and avoiding excessive noise exposure reduces the risk of deafness. Removing wax and foreign bodies, and treating infections and glue ear promptly helps improve hearing or prevent further damage. Hearing aids, and for some people cochlear implants (an operation to replace a damaged cochlear with an artificial device) can enable hearing.

Aids to communication: The ability to communicate is an essential part of living in human society. Advances in technology have led to an explosion of devices, gadgets and other methods to help people with hearing loss listen to and talk to others. Older people are often reticent about using a hearing aid, perhaps reluctant to accept the physical effects of ageing, or concerned about the stigma of deafness or the rough deal that deaf people often get from society. Modern hearing aids are a great improvement on those that were available just a couple of decades ago, but they rarely restore hearing to normal and don't suit or help everyone. Many people with hearing loss find it useful to develop other means of communication. Even those with a mild 25 to 40 decibel loss find lip-reading useful, while people with severe hearing loss (70 to 95 decibels) often struggle to follow speech even with a hearing aid and may use other communication methods, such as lip-reading, sign language, sign-supported English, cued speech, speech-to-text, text phones and text messaging.