Hearing loss is the result of sound signals not reaching the brain. There are two main types of hearing loss, depending on where the problem lies.

• Sensorineural hearing loss is caused by damage to the sensitive hair cells inside the inner ear or damage to the auditory nerve. This occurs naturally with age or as a result of injury.
• Conductive hearing loss happens when sounds are unable to pass from your outer ear to your inner ear, often because of a blockage such as earwax or glue ear.

These causes are explained below.

Age

Age is the biggest single cause of hearing loss. Hearing loss that develops as a result of getting older is often known as age-related hearing loss or presbycusis.

Most people begin to lose a small amount of their hearing from around 40 years of age. This hearing loss increases as you get older. By the age of 80, most people have significant hearing problems.

As your hearing starts to deteriorate, high-frequency sounds, such as female or children’s voices, may become difficult to hear. It may also be harder to hear consonants such as "s", "f" and "th". This can make understanding speech in background noise very difficult.

Loud noises

Another common cause of hearing loss is damage to the ear from repeated exposure to loud noises over time. This is known as noise-induced hearing loss, and it occurs when the sensitive hair cells inside the cochlea become damaged.

You're at higher risk of developing noise-induced hearing loss if you:

• work with noisy equipment, such as pneumatic drills or compressed-air hammers
• work in environments where there's loud music, such as a nightclub
• regularly listen to music at a high volume through headphones

Hearing loss can also occur suddenly after exposure to an exceptionally loud noise, such as an explosion. This is known as acoustic trauma.

See preventing hearing loss for advice on reducing your risk of noise-induced hearing loss.

Other types of sensorineural hearing loss

Sensorineural hearing loss occurs if the sensitive hair cells inside the cochlea are damaged, or as a result of damage to the auditory nerve (which transmits sound to the brain). In some cases, both may be damaged.

Hearing loss caused by age and exposure to loud noises are both types of sensorineural hearing loss.

Sensorineural hearing loss can also be caused by:

• the genes you inherit – some people may be born deaf or become deaf over time because of a genetic abnormality
• viral infections of the inner ear – such as mumps or measles
• viral infections of the auditory nerve – such as mumps or rubella
• Ménière's disease – where a person suffers with vertigo, spells of hearing loss, tinnitus and the feeling of a blockage in the ear
• acoustic neuroma – a non-cancerous (benign) growth on or near the auditory nerve
• meningitis – an infection of the protective membranes that surround the brain and spinal cord
• encephalitis – inflammation of the brain
• multiple sclerosis – a neurological condition affecting the central nervous system (brain and spinal cord)
• a head injury
• an autoimmune condition
• malformation of the ear
• stroke – where the blood supply to the brain is cut off or interrupted

Some treatments and medicines, such as radiotherapy for nasal and sinus cancer, certain chemotherapy medicines or certain antibiotics can also damage the cochlea and the auditory nerve, causing sensorineural hearing loss.

People with diabetes, chronic kidney disease and cardiovascular disease are also at increased risk of hearing loss.

Sensorineural hearing loss is permanent and hearing aids are often required to improve hearing in these cases. Read more about treating hearing loss.

Causes of conductive hearing loss

Conductive hearing loss is usually caused by a blockage, such as having too much ear wax, a build-up of fluid in the ear (glue ear), or an ear infection.

Conductive hearing loss can also be caused by:

• a perforated eardrum – where the eardrum is torn or has a hole in it
• otosclerosis – an abnormal growth of bone in the middle ear which causes the inner hearing bone (the stapes) to be less mobile and less effective at transmitting sound
• damage to the hearing bones from injury, a collapsed ear drum or conditions such as cholesteatoma
• swelling around the eustachian tube – caused by jaw surgery or radiotherapy for nasal and sinus cancer
• malformation of the ear
• Eustachian tube dysfunction
• something becoming trapped in the ear (a foreign body)

Conductive hearing loss is usually temporary and can often be treated with medication or minor surgery. Read more about treating hearing loss.