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Types and causes of hearing loss

Conductive and sensorineural hearing loss

There are two main types of hearing loss – conductive and sensorineural.

It is possible to have both types present at the same time – something called a 'mixed' hearing loss. More rarely, hearing loss can result from damage to the auditory part of the brain.

Conductive hearing loss is the result of sounds not being able to pass freely to the inner ear. This usually results from a blockage in the outer or middle ear, such as a build-up of excess ear wax or fluid from an ear infection (especially common in children). It can also happen as a result of some abnormality in the structure of the outer ear, ear canal or middle ear – or be due to a ruptured eardrum.

A condition known as otosclerosis (which results in the abnormal growth of bone in the middle ear) can cause severe conductive hearing loss. The excess bone prevents the ossicles in the middle ear from moving freely.

The result of this type of hearing loss is that sounds become quieter, although not usually distorted. Depending on its cause, a conductive hearing loss can either be temporary or permanent.

Conductive hearing losses can often be corrected with medical management, or minor surgery.

This type of hearing loss is sometimes referred to as sensory, cochlear, neural or inner ear hearing loss.

A permanent sensorineural hearing loss is the result of damage to the hair cells within the cochlea or the hearing nerve (or both). Damage to the cochlea occurs naturally as part of the ageing process (age-related hearing loss is known as presbycusis) – but there are many things that cause sensorineural hearing loss, or add to it, such as:

  • Regular and prolonged exposure to loud sounds. These sounds do not necessarily have to be unpleasant – for example, exposure to loud music can be just as harmful as exposure to loud machinery. Even short term exposure to loud sound can cause temporary deafness.
  • Ototoxic drugs – some medicines are harmful to the cochlea and/or hearing nerve. These include drugs that are used in the treatment of serious diseases such as cancer but also include certain types of antibiotics
  • Certain infectious diseases, including Rubella
  • Complications at birth
  • Injury to the head
  • Benign tumours on the auditory nerve - although rare, these can cause hearing loss
  • Genetic predisposition – some people are especially prone to hearing loss.

Sensorineural hearing loss not only changes our ability to hear quiet sounds, but it also reduces the quality of the sound that is heard, meaning that individuals with this type of hearing loss will often struggle to understand speech. Once the cochlea hair cells become damaged, they will remain damaged for the rest of a person’s life. Therefore sensorineural hearing loss is irreversible and cannot be cured – at least at the present time.

Research breakthrough. Human stem cells restore hearing.

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