Inner ear damage
Tinnitus is often related to damage that occurs inside the inner ear.
Sounds pass from the outer ear through the middle ear to the inner ear, which contains the cochlea and auditory nerve. The cochlea is a coiled, spiral tube with a large number of sensitive hair cells. The auditory nerve transmits sounds to the brain.
If part of the cochlea is damaged, it will stop sending information to parts of your brain. These areas of the brain will then actively 'seek out' signals from parts of the cochlea that still work. These signals are over-represented in the brain and cause the sounds of tinnitus.
In older people, tinnitus is often caused by natural hearing loss, which makes the hearing nerves less sensitive. In younger people, tinnitus can sometimes occur as a result of hearing damage caused by excessive noise.
Other causes
As well as natural hearing loss and inner ear damage, there are several other possible causes of tinnitus. These include:
•a build-up of earwax that blocks the ear
•a middle ear infection (otitis media)
•glue ear (otitis media with infusion)
•otosclerosis - an inherited condition where an abnormal bone growth in the middle ear causes hearing loss
•Ménière's disease - a condition that affects part of the inner ear known as the labyrinth and causes balance problems
•otosclerosis - a growth of spongy bone in the inner ear that causes progressive hearing loss
•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
•a perforated eardrum
Rarer causes
Less commonly, tinnitus may also develop as a result of:
•a head injury
•exposure to sudden or very loud noise, such as an explosion or gunfire
•acoustic neuroma - a rare, non-cancerous growth that affects the hearing nerve in the inner ear
•adverse reactions to certain medications, such as antibiotics, diuretics, quinine and aspirin (this is more likely to occur when the recommended dosage is exceeded)
•solvent abuse, drug misuse and alcohol misuse
•high blood pressure (hypertension) and narrowing of the arteries (atherosclerosis)
•an overactive thyroid gland (hyperthyroidism)
•Paget's disease - where the normal cycle of bone renewal and repair is disrupted
