Hearing loss is very common. It can be very distressing, particularly if it is getting worse and especially if it affects both ears. Everyone's hearing gets worse as they get older. However, there are many types of hearing loss and not all are restricted to older people. In this article we talk about the different causes of hearing loss, their different characteristics and what you can do about them.
Structure of the ear
The ear is roughly divided into three parts. The outer (external) ear includes the part you can see (called the pinna) and the narrow tube-like structure (the ear canal), which your health professional can look down with a torch. At the end of the canal is the eardrum. This separates the external ear from the middle ear. The eardrum is a tightly stretched membrane, a bit like the skin of a drum.
The middle ear is an air-filled compartment. Inside it are the three smallest bones in the body, called the malleus, incus and stapes. These bones are connected to each other. The last in the line, the stapes, also makes contact with the inner (internal) ear. The air space of the middle ear connects to the back of the nose by the Eustachian tube.
The inner ear is made up of two components, the cochlea and the vestibular system. The cochlea is involved with hearing. The vestibular system helps with balance. The cochlea is a snail-shaped chamber filled with fluid. It is lined with special sensory cells called hair cells. These cells transform sound waves into electrical signals. The cochlea is attached to a nerve that leads to the brain.
The vestibular system is made up of a network of tubes, called the semicircular canals, plus the vestibule. The vestibular system also contains special sensory cells but here they detect movement instead of sound. Both the cochlea and the vestibular system are connected to a nerve which carries electrical signals to the brain.
How do we hear?
Sound waves are created when air vibrates. To hear, the ear must change sound into electrical signals which the brain can interpret. The outer part of the ear (the pinna) funnels sound waves into the ear canal. When sound waves reach the eardrum they make it vibrate. Vibrations of the eardrum make the tiny bones in the middle ear move too. The last of these bones (the stapes) passes on the vibrations to the fluid-filled chamber called the cochlea. When the vibrations reach the cochlea, the fluid inside it moves. As the fluid moves it vibrates the hairs on the cells that line the cochlea. Each cell is stimulated by a particular note (or frequency) of sound. The vibration of the hair cells is turned into an electrical signal by the organ of Corti, at their base. The organ of Corti then sends signals down the hearing (auditory) nerve to the brain. Special areas in the brain receive these signals and translate them into what we know as sound.
Your ears create electrical signals that represent an extraordinary variety of sounds. For example, the speed at which the eardrum vibrates varies with different types of sound. With low-pitched sounds the eardrum vibrates slowly. With high-pitched sounds it vibrates faster. This means that the special hair cells in the cochlea also vibrate at varying speeds. This causes different signals to be sent to the brain. This is one of the ways in which we are able to distinguish between a wide range of sounds.
What can cause hearing loss?
Damage to any part of the ear can cause a hearing loss.
Conductive hearing loss
If there is a problem in the ear canal or the middle ear, this causes what is known as a conductive hearing loss. In conductive hearing loss, the movement of sound (conduction) is blocked or does not pass into the inner ear. This is often as the result of earwax (cerumen) or fluid in the middle ear, although it may also be caused by a burst (ruptured) eardrum or by otosclerosis (see below).
Sensorineural hearing loss
If the fluid-filled chamber called the cochlea or the hearing nerve is not working properly this causes what is known as a sensorineural hearing loss. Usually this means that hair cells in the cochlea are not working properly or there is a problem with the hearing nerve so that some or all sounds are not being sent to the brain. It does not usually affect the entire range of sound frequencies, at least not at first. Sensorineural hearing losses are usually permanent. They can be mild, moderate, severe or profound and affect one or both ears.
It is also possible for sensorineural and conductive hearing losses to occur together in a mixed hearing loss.
Causes of conductive hearing loss: the eardrum and ear canal
Blockage of the ear canal
The most common cause of blockage in the ear canal is earwax (cerumen). See separate leaflet called Earwax for more details.
Something in the ear canal
Objects that shouldn't be there (foreign bodies) are most often found in the ears of children. Peas, beads or small pieces of a toy are the most common foreign bodies to block the ear and affect hearing.
It is usually best to have the object removed. This is done either by syringing it out with warm water or with a special extracting device.
Sometimes the skin of the ear canal can become inflamed. This may be caused by infection, allergy or other causes. Common symptoms include itch, ear discharge and dulled hearing. It is treated with ear drops. See separate leaflet called Ear Infection (Otitis Externa) for more details.
A torn (perforated) eardrum is not usually serious and often heals on its own without any complications. It may cause hearing loss, in which case a small procedure to repair it is an option. See separate leaflet called Perforated Eardrum for more details.
Scarring of the drum is usually due to repeated perforation, either by infection or by poking objects into the ear.
Cholesteatoma is an uncommon condition where a growth develops in the ear. You can be born with it but usually it occurs as a complication of a long-standing (chronic) ear infection. The most common symptoms are a loss of hearing and a smelly discharge from the ear. See separate leaflet called Cholesteatoma for more details.
The need for an eardrum
Not having an eardrum does not result in deafness. Part of the job of the eardrum is to boost (amplify) sound. Without the eardrum the sound will still reach the middle ear; however, it will not be as loud. Its other job is to seal off the middle ear and prevent it from damage by water and soap.
Causes of conductive hearing loss: the middle ear
The middle ear consists of an air space and the three small hearing bones (ossicles). Conduction of sound through the middle ear depends upon both of these.
The air in the middle ear gets there from the Eustachian tube, which links the middle ear to the throat. The tube allows air in and out (the ear popping sensation on a flight shows this happening). This allows the air pressure inside the ear to equalise with that outside and replaces air that gets absorbed by the cells lining the middle ear.
The middle ear system can therefore be affected by problems affecting the Eustachian tubes and the middle ear space itself and by problems affecting the hearing bones.
Conditions affecting the air space
Eustachian tube dysfunction
When your Eustachian tube isn't working properly this can dull your hearing. It is usually a temporary problem that lasts a week or so and most commonly happens during or after a cold. The middle ear can fill with fluid. This is called a middle ear effusion. See separate leaflet called Eustachian Tube Dysfunction for more details.
Glue ear happens when the middle ear fills with a glue-like liquid instead of air. Usually it clears without treatment. However, an operation to clear the fluid and put in a tiny tube (grommet) to allow air to get into the middle ear may be advised if it persists. See separate leaflet called Glue Ear for more details.
An ear infection is very common, particularly in children. The main symptoms are earache and feeling unwell but it can cause temporary hearing loss. See separate leaflet called Ear Infection (Otitis Media) for more details.
Conditions affecting the hearing bones
Otosclerosis is the most common cause of hearing loss in young people. It mainly affects the third of the three bones in the middle ear (the stapes). It causes gradual hearing loss. Treatments include hearing aids and surgery. See separate leaflet called Otosclerosis for more details
Causes of sensorineural hearing loss: the cochlea
Hearing loss of older people (presbyacusis)
The most common cause of hearing loss is age-related. Most people over the age of 60 develop hearing loss to some degree. The exact cause is not known but it is thought to be due to the cells in the cochlea becoming damaged over time. A hearing aid may be needed. See separate leaflet called Hearing Loss of Older People (Presbyacusis) for more details.
Loud noise damages the cochlea and can result in permanent hearing loss and ringing in the ears (tinnitus). The risk is based on how loud the noise is and how long you have been exposed to it. Those who work with loud equipment - people who shoot, use pneumatic drills or operate heavy machinery - should always wear their protective ear-wear in order to prevent long-term damage. The cumulative effect of prolonged exposure to loud noise speeds up the process of hearing loss. Loud noise from MP3 players and music gigs is thought to be the reason why hearing loss is increasingly affecting young people.
If you ever have ringing in your ears or dull hearing after listening to music, it was too loud; many musicians now wear ear filters to protect their hearing.
Other causes of cochlear damage
The cochlea can be damaged by a severe head injury. Such trauma can also disrupt the tiny ear bones (the ossicles) and cause hearing loss that way. The cochlea can be damaged by a cholesteatoma (see above).
Some infections may damage the hearing nerves and/or the cochlea. These include measles, mumps, bacterial and viral meningitis and tuberculosis. The zoster virus, which causes shingles, can affect the hearing nerves. In all of these cases the resulting loss of hearing can be permanent.
The cochlea is also vulnerable to damage by poisonous substances (toxins). This includes some medicines which can damage the hearing. Certain antibiotics are known to carry a risk of this but they may still be used where nothing else will work, particularly if life is at risk. The small risk of hearing nerve damage is felt to be outweighed by the need for the medicine. One example is gentamicin, an antibiotic which is invaluable in severe infections by particular germs (bacteria), especially in babies. Any baby who is treated with gentamicin will automatically have a hearing nerve testing once they have recovered from the infection.
Ménière's disease causes attacks of dizziness and tinnitus, as well as hearing loss. See separate leaflet called Ménière's Disease for more details.
Causes of sensorineural hearing loss: the auditory nerve and the brain
Conditions affecting the hearing (auditory) nerve
An acoustic neuroma is a rare growth on the hearing nerve inside the skull. The hearing loss that an acoustic neuroma causes affects just one ear. See separate leaflet called Acoustic Neuroma for more details.
Conditions affecting the brain
Ultimately, sound is heard and interpreted by the brain; conditions that affect the hearing centre in the brain can also cause hearing loss. Examples would be brain injury through trauma, stroke, brain infection (encephalitis) and multiple sclerosis. In some cases there might be partial or even complete recovery over time, although in other cases the loss would be permanent.
Congenital hearing loss
Congenital hearing loss is hearing loss present at birth or soon after. Most of it is inherited but about 1 in 4 cases are due to things that happen to the baby in the womb. This includes infections (such as German measles or cytomegalovirus) and being premature or not getting enough oxygen at birth. Microtia is a condition in which the ear is underdeveloped or does't develop at all.
There are many inherited (genetic) syndromes which may cause hearing loss. These include Down's syndrome, Treacher Collins' syndrome and Waardenburg's syndrome. They may have their effects through the mechanisms described in this leaflet, although in some cases they are due to abnormal development of the hearing apparatus in the womb.
Some inherited hearing loss in children is not present at birth but develops in the early years. The first sign can be poor speech development. In the UK all newborn babies have a hearing test to make sure the hearing (auditory) nerve is working properly. Babies are checked again at about 8 months of age to make sure they can still hear. Families are encouraged to talk to health visitors or doctors if their child's speech seems delayed; most cases are detected fairly quickly.
In many cases treatment to improve hearing is possible. This might involve hearing aids, cochlear implants or tiny tubes called grommets. In cases of profound deafness, where hearing cannot be improved, children and their families are taught how to use sign language from a very early age in order to help communication.
Unilateral versus bilateral hearing loss: one ear or two?
The most common causes of hearing loss, such as age-related hearing loss, tend to affect both ears. However, this is often unequal, with the hearing loss of the ears differing from one another. Some people will have hearing aids fitted to just one ear, whereas others will choose to aid both ears.
Loss of hearing in just one ear is sometimes called single-sided deafness (SSD) or hearing loss. Being deaf in one ear presents particular challenges:
- It affects directional hearing - that is, the ability to work out which direction sound is coming from. This is also called spatial hearing. If you have normal hearing, you use the time difference in a sound arriving at each ear and the difference in loudness between two ears, to work out where a sound is coming from and how far away it is. If you have significant hearing loss in just one ear this makes it much harder to localise a sound. For example, hearing someone call you outside or hearing whether a car is coming when you are about to cross the road.
- When a sound is coming from your affected side, your head gets in the way of the sound getting to your good ear - the head shadow effect. This is particularly noticeable with higher-pitched sounds such as the c, f, p, s, t, ch and sh sounds, making it harder to discriminate between some words. This is why people with single-sided hearing loss have problems hearing speech when there is background noise, even when the hearing is normal in their other ear.
If you are affected by one-sided hearing loss, here are some coping strategies that may help:
- Don't be afraid to tell people that you are deaf in one ear or that you hear much better in one ear than in the other.
- Always make sure people are seated or walk on your good side.
- If there is background noise coming from only one direction, put yourself so that the noise is to your bad ear.
- If your affected ear is on the passenger side of your car, seating someone behind you rather than next to you may help.
- If you are going to a meeting, arrive early enough to choose a seat so that most people are on your good side. (This is easier at a rectangular rather than a round table - for example, in the corner with your back to a wall.)
- Remind your friends, family, teachers and co-workers not to expect you to answer if they call your name in a crowded place or across a road; otherwise they may think you are brusque or aloof and ignoring them.
- Keep your mobile phone in your pocket, as locating it when it rings can be very hard.
- Use a mono-splitter to listen to stereo music.
- Enjoy being able to sleep in a noisy environment by sleeping on your 'good' side!
Bone-anchored hearing aid (BAHA) and contralateral routing of signal (CROS) hearing aids are specifically designed for people with one-sided hearing loss. They pipe the sounds from your 'bad ear' side to your good or better side.
Protecting your hearing
The best way to protect your hearing is to avoid exposure to very loud noise completely and to limit the amount of time you are exposed to loud noise. Hearing loss can be disabling and can lead to feelings of isolation and depression.
Discussing your hearing loss with your doctor
If you think you are losing hearing then discuss this with your GP. You may notice difficulty distinguishing what people are saying, or that everything seems quieter. Others may comment that you have the TV turned up very loud. Perhaps you have been exposed to loud noise.
Your doctor may ask you the following questions:
- Has your hearing worsened suddenly or gradually? Sudden deafness is uncommon but can be due to sudden trapping of water behind wax (cerumen) in the ear canals. Rarely it can have a more serious cause and you may need to see a hearing specialist urgently.
- Are both ears affected? Clearly ear infections, glue ear and earwax may be one-sided or two-sided. However, if you have severe hearing loss and wax is present in the ear canals then the wax needs to be cleared. After this the ear needs to be reassessed in case the wax was not the only reason for hearing reduction.
- Do you have associated sinus problems/congestion? If so glue ear is very likely. This may be following a cold, when mucus remains in the middle ear space for several weeks. It may also be associated with allergic conditions such as hay fever.
- Have you been exposed to loud noise? Are you aged over 50 years? Either of these increases the chance that this is age-related high-frequency hearing loss.
- Do you have particular difficulties with hearing conversation? Again this is a feature of high-frequency hearing loss, as consonants, which make language clear, are higher-frequency sounds than vowels.
- Is there a family history of hearing loss? Some causes of deafness run in families, particularly otosclerosis.
Your doctor is likely to perform some tests on your hearing in the surgery to decide whether your hearing loss seems to be conductive, sensorineural, or mixed. They will examine your ears for wax and for obvious problems affecting the eardrum. They may then refer you for formal hearing tests. See separate leaflet called Hearing Tests for more details.
There are many causes of hearing loss: the most common in younger people is otosclerosis, whereas the most common in older people is hearing loss of older people (presbyacusis). Many people have mixed hearing loss: you may have hearing loss of older people and earwax (cerumen) for instance, or otosclerosis and earwax. It's very important, if your doctor finds a simple cause for your reduced hearing and treats it, that you return to your doctor if your hearing is still not better. Many conditions are treatable and a very few need urgent management.
Dr Mary Lowth
Dr Jacqueline Payne
Dr Helen Huins