Bell's palsy - What is it?

If you have Bell's palsy, the muscles of your face suddenly become weak. This usually happens on just one side of the face. It means you can't move your face properly. You may find only half of your face moves when you smile, and you can't move one eyelid to open or close it.

The most common symptom of Bell's palsy is not being able to move the muscles on one side of your face. Bell's palsy happens because one of the nerves sending messages from your brain to your face muscles has stopped working properly.

Some people who have a stroke also get weakness in the muscles of the face. But this is different from Bell's palsy. If you have a stroke, other parts of your body are affected too. And after a stroke you can usually move your forehead and eyelids.

Bell's palsy happens when a nerve in your face is damaged.[1] It's called the facial nerve. There's one on each side of your face.

Each facial nerve comes out from your brain through a small tunnel under your ear, and then divides into many branches. These branches are connected to the muscles that you use to blink, smile and frown.

The nerves also go to the glands that make your tears and saliva, and they carry the sense of taste from your tongue.

We don't know for certain what causes Bell's palsy.

Doctors think there may be swelling (inflammation) around the facial nerve, which squashes the nerve as it passes through your skull. The nerve can't work properly until the inflammation goes. The messages the brain sends to your face muscles get interrupted. So the muscles of your face become weak or paralysed (they can't move).

Facial nerves control the movement of the muscles in your face and send messages back to the brain. Doctors think the swelling around the nerve is probably caused the by the same viruses that cause cold sores and chickenpox:[2] The virus that causes cold sores is called herpes simplex virus. The virus that causes chickenpox is called herpes zoster virus. Bell's palsy caused by herpes zoster virus is less common but can be more serious.[3]

You might have had cold sores or chickenpox in the past. But some people have these viruses for a long time without getting any symptoms. Getting Bell's palsy does not mean you will go on to get cold sores or chickenpox.

Not everyone who has weak face muscles has Bell's palsy. About 30 in 100 people have another reason for their muscle weakness.[4] These include:

A stroke
An injury
An ear disease
Lyme disease (caused by a tick bite)
A type of cancer (but this is rare).

Your doctor will examine you and ask you questions to rule out other possible reasons for your face muscles becoming weak. You won't be diagnosed with Bell's palsy until other problems have been ruled out. There isn't a test that can tell you for certain you have Bell's palsy. But you can have investigations to look for other things that might make your face muscles weak. You might need to go to hospital for an MRI scan or a CT scan. And you might also need a test called electromyography (EMG) to see how badly your nerve is damaged.

References

National Institute of Neurological Diseases and Stroke (NINDS) Bell's palsy fact sheet. Available at http://www.ninds.nih.gov/disorders/bells/detail_bells.htm. Last accessed 16 January 2006.
Murakami S, Mizobuchi M, Nakashiro Y, et al. Bell palsy and herpes simplex virus: identification of viral DNA in endoneurial fluid and muscle. Annals of Internal Medicine. 1996; 124: 27-30.
Adour KK, Byl FM, Hilsinger RL Jr, et al. The true nature of Bell's palsy: analysis of 1,000 consecutive patients. Laryngoscope. 1978;88:787"801.
Holland NJ, Weiner G. Recent developments in Bell's palsy. BMJ. 2004;329:553-557.

Glossary

stroke: You have a stroke when the blood supply to a part of your brain is cut off. This damages your brain and can cause symptoms like weakness or numbness on one side of your body. You may also find it hard to speak if you've had a stroke.
gland: A gland is any group of cells in the body that makes and releases something for use by another part of the body. For example, the thyroid gland makes a hormone called thyroxine. This acts on receptors within cells. By acting on the receptors it gives the cells a message to speed up their metabolism and work harder.
inflammation: Inflammation is when your skin or some other part of your body becomes red, swollen, hot and sore. Inflammation happens because your body is trying to protect you from germs, from something that's in your body and could harm you (like a splinter) or from things that cause allergies (these things are called allergens). Inflammation is one of the ways in which your body heals an infection or an injury.
chickenpox: Chickenpox is a common childhood illness caused by a virus. It usually leads to a fever, tiredness and an itchy rash. The virus can easily spread from person to person, and people usually get it about two weeks after they were near someone with the illness. About two days before the rash starts, you can give the virus to others. Chickenpox clears up on its own in most children, but adults and some children may get complications such as pneumonia, kidney problems or heart problems. In the UK, people aren't usually immunised against chickenpox unless they have an immune disease (or another disease that would make infection dangerous for them).
Lyme disease: Lyme disease is an infection transmitted by the bites of certain ticks. Lyme disease can lead to severe, flu-like symptoms, including fatigue, fever, headache, muscle pain and a rash. Lyme disease can be treated with antibiotics. In rare cases, if the infection is not treated, people can get more serious problems, such as arthritis in their joints and problems with their nervous system and heart.
MRI scan: A magnetic resonance imaging (MRI) machine uses a magnetic field to create detailed pictures of the inside of your body.
CT scan: A CT scan is a type of X-ray. It takes several detailed pictures of the inside of your body from different angles. CT stands for computed tomography. It is also called a CAT scan (computed axial tomography).

This information does not replace medical advice. If you are concerned you might have a medical problem please ask your Boots pharmacy team in your local Boots store, or see your doctor.