They do not correct hearing loss, they only amplify sounds to help people hear.
3 main types exist:

• behind the ear
• in the ear
• on the body

Each year brings an improvement in hearing aid design and performance. If your hearing aid is more than 2 years old and appears less effective than when you first received it, then you should return to the hearing aid dispenser or clinic which prescribed it for a check-up.

Conductive Deafness
Conductive Deafness arises from any defect or blockage in those parts of the ear which conduct sound to the inner ear i.e.. any defect or blockage in the outer or middle ear. This type can often be helped or remedied medically or surgically. It is also the type of deafness that can be most easily helped by amplification. Unfortunately those suffering from conductive deafness often suffer from that plus some nerve deafness which complicates the choice of hearing aid. Such deafness is named 'Mixed Deafness'.

Conductive deafness occurs in the external auditory canal (ear canal) or in the middle ear. This may be as a result of:

• a blockage in the ear canal such as wax;
• glue ear;
• eardrum perforation;
• otosclerosis – the tiny bones in the middle ear are too stiff.

Conductive deafness is often treatable.

Sensori-Neural Deafness is sometimes called 'nerve deafness' or 'perceptive deafness'.

Sensori-Neural hearng loss results from damage to the hair cells, nerve fibers or both in the inner ear. This is the most common type of hearing loss and is often caused by aging or prolonged exposure to noise. It also can be caused by high fever, birth defects and certain drugs. People with sensori-neural hearing loss can hear speech, but frequently have difficulty understanding it. The problem is usually compounded when background noise is present. Sensori-neural hearing loss is most commonly treated by the use of a hearing instrument, and generally cannot be corrected through surgery or medicine

Sensori-neural deafness is due to reduced function of the inner ear (cochlea, the part that converts sound waves and passes them to the brain) or the nerve fibres leading to the brain.

The causes of sensori-neural hearing loss are:

• loud noise;
• ageing;
• some drugs;
• childhood disease etc.