Tinnitus

It's not clear exactly what causes tinnitus, but it's thought tobe a problem with how the ear hears sounds and how the brain interprets them.

Many cases are associated with Hearing impairment caused by damage to the inner ear, although around one person in every three with the condition doesn't have any obvious problem with their ears or hearing.

Inner eardamage

Sounds pass from the outer ear through to the inner ear, which contains thecochlea and auditory nerve. The cochlea is a coiled, spiral tube containing a large number of sensitive hair cells. The auditory nerve transmits sound signals to the brain.

If part of the cochlea is damaged, it will stop sending information to your brain. Thebrainmay then actively "seek out" signals from parts of the cochlea that still work. These signalsmight thenbecome over-represented in the brain, whichmay cause the sounds of tinnitus.

In older people, damage to the cochlea often occurs naturally with age. In younger people, it can be caused byrepeated exposure to excessive noise.

Other causes

As well as inner eardamage, there are several other possible causes of tinnitus. These include:

• an earwax build-up that blocksthe ear
• a middle ear infection
• glue ear a build-up of fluid in the middle ear
• a perforated eardrum
• Mnire's disease a condition that also causes hearing loss and vertigo (a spinning sensation)
• otosclerosis an inheritedcondition where an abnormal bone growth in the middle ear causes hearing loss

Rarer causes

Less commonly, tinnitus may develop as a result of:

• a head injury
• exposure to a sudden or very loud noise, such as an explosion orgunfire
• anaemia a reduced number of red blood cells that can sometimes cause the blood to thin and circulate so rapidly that it produces a sound
• reactions to certain medications, such as some chemotherapy medicines, antibiotics , diuretics, non-steroidal anti-inflammatory drugs (NSAIDs) and aspirin (this is more likely to occur at very high doses)
• acoustic neuroma a rare non-cancerous growth that affects the hearing nerve in the inner ear
• high blood pressure (hypertension) andnarrowing of the arteries (atherosclerosis)
• an overactive thyroid gland (hyperthyroidism) or underactive thyroid gland (hypothyroidism)
• diabetes
• Paget's disease where the normal cycle of bone renewal and repair is disrupted