Bell’s palsy occurs when the nerve that controls the facial muscles (facial nerve) becomes inflamed or compressed. It is not known what causes the facial nerve to become inflamed, although it is thought that a virus, possibly a herpes virus, may be responsible.

The facial nerve

The facial nerve passes through a narrow gap of bone near the upper jaw on its way from the brain to the face. If the facial nerve is compressed or swollen it can interfere with the signals that your brain sends to the muscles in your face.

This interference can restrict the blood and oxygen supply to your nerve cells and cause the facial weakness or paralysis that is characteristic of Bell’s palsy.

Herpes virus

The types of herpes virus thought to cause inflammation of the facial nerve are:

• the herpes simplex virus (HSV), including either herpes type 1 (HSV-1), which causes cold sores, or herpes type 2 (HSV-2), which causes genital herpes
• the varicella-zoster virus, which causes chickenpox and shingles

The varicella-zoster virus is a less common cause of Bell’s palsy than the herpes simplex virus, but can lead to the more serious condition called Ramsay Hunt Syndrome.

Read more about complications of Bell’s palsy.

In addition to herpes, Bell’s palsy has also been linked with other viral infections.

As a complication of pneumonia

Bell’s palsy is thought to occasionally occur as a complication of pneumonia.

A number of complications can occur as a result of Bell’s palsy, depending on the extent of nerve damage.

About 2 in 10 people experience long-term problems resulting from Bell’s palsy, which may include any of the following:

• A contracture – This is where your facial muscles are permanently tense. It can lead to facial disfigurement such as the eye becoming smaller, the cheek becoming more bulky, or the line between the nose and the mouth becoming deeper.
• Loss or reduced sense of taste – This can happen if any damaged nerves do not repair properly.
• Speech problems – This can occur as a result of damage to the facial muscles.
• Eye-mouth synkinesias – This happens as a result of the nerve in your face growing back in a different way. It can cause your eye to wink when eating, laughing or smiling. Sometimes it can become so severe that the eye can close completely during meals.
• Eye drying and corneal ulceration – Corneal ulceration can occur when the eyelid is too weak to close completely and the protective tear film becomes less effective. It can also occur as a result of reduced tear production, which can lead to infection and cause blindness.
• Tears when eating, known as ‘crocodile tears’

Long-term complications of Bell’s palsy are more likely to happen if:

• you have been affected by a complete palsy, resulting in no movement at all (paralysis) on one side of your face
• you are over 60 years of age
• you had severe pain when you first experienced symptoms
• you have high blood pressure
• you have diabetes
• you are pregnant
• your facial nerve is badly damaged
• you have not started to recover after six weeks

Ramsay Hunt syndrome

If you have Bell’s palsy that was caused by the varicella-zoster virus, there is a possibility that you could develop a more serious condition called Ramsay Hunt syndrome. However, this condition is rare, with fewer than 2 in 100 people with Bell’s palsy being affected.

Ramsay Hunt syndrome can cause blisters to appear on your tongue and the inside of your ears. It can usually be treated with steroids and antiviral medication.

There is no specific test to diagnose Bell’s palsy. However, tests can be used to rule out other conditions that cause facial paralysis.

You should visit your nearest A&E department immediately or call 999 for an ambulance if you or someone you are with develops sudden facial paralysis so a doctor can determine the cause.

Studies have also shown that treatment for Bell’s palsy is most effective if it is started quickly, within 72 hours of symptoms developing.

Ruling out other conditions

Bell’s palsy is diagnosed using a process known as diagnosis by exclusion. Your doctor will look for any evidence that might suggest your symptoms are caused by a different health condition, such as:

• Lyme disease: a bacterial infection caused by ticks
• a tumour: an abnormal tissue growth
• Moebius syndrome: a rare condition that is present from birth (congenital)
• stroke
• middle ear infection
• cholesteatoma (an abnormal collection of skin cells in the middle ear) 
• head injury

Your doctor will examine your head, ears and neck. They will also check the muscles in your face to determine whether it is only the facial nerve that has been affected.

If your doctor is unable to find evidence of symptoms that are associated with other conditions, Bell’s palsy may be diagnosed.

Further testing

If your doctor is still uncertain, they may refer you to an ear, nose and throat (ENT) specialist for further testing. You may have electromyography or an imaging scan. These are explained below.

Electromyography

During electromyography (EMG), a very thin needle electrode is inserted through the skin and into your muscle. A machine called an oscilloscope is then used to measure the electrical activity in your muscles and nerves. The information provided by an EMG can be used to assess the extent of any nerve damage.

Imaging scans

Imaging scans such as magnetic resonance imaging (MRI) may be used to determine the cause of the pressure on your facial nerve. MRI scans use radio waves and a strong magnetic field to produce a detailed image of the inside of your body.

A computerised tomography (CT) scan may also be used to detect other causes of your symptoms, such as an infection or tumour. A facial CT scan may also be carried out to rule out facial fractures.

Bell’s palsy is a condition that causes temporary weakness or paralysis of the muscles in one side of the face. It is the most common cause of facial paralysis.

What are the symptoms?

The symptoms of Bell’s palsy vary from person to person. The weakness on one side of the face can be described as either:

• partial palsy, which is mild muscle weakness
• complete palsy, which is no movement at all (paralysis) – although this is very rare

Bell’s palsy can also affect the eyelid and mouth, making it difficult to close and open them and in rare cases, it can affect both sides of a person’s face.

Read more about the symptoms of Bell’s palsy

When to seek medical advice

As well as being a symptom of Bell’s palsy, facial weakness or paralysis can also be a sign of a more serious condition – such as a stroke.

Therefore, you should visit your nearest A&E department immediately or call 999 for an ambulance if you or someone you are with develops sudden facial paralysis so a doctor can determine the cause.

Bell’s palsy is only diagnosed if other possible causes of your symptoms are ruled out.

Read more about diagnosing Bell’s palsy.

Why does it happen?

Bell’s palsy is believed to occur when the nerve that controls the muscles in your face becomes compressed.

The exact cause is unknown, although it’s thought to be because the facial nerve becomes inflamed, possibly due to a viral infection. Variants of the herpes virus may be responsible.

Read more about the causes of Bell’s palsy

Who is affected?

Bell’s palsy is a rare condition that affects about 1 in 5,000 people a year. It more commonly affects those aged between 15 and 45, but people outside this age group can also suffer from the condition. Both men and women are affected equally.

Bell’s palsy is more common in pregnant women and those with diabetes and HIV, for reasons that are not yet fully understood.

Treating Bell’s palsy

Around 7 out of 10 people with Bell’s palsy make a complete recovery, with or without treatment.

Most people notice an improvement in their symptoms after about two to three weeks. However, a complete recovery can take between three and six months. The recovery time varies from person to person and will depend on the amount of nerve damage.

Steroids, usually prednisolone, are used to reduce the swelling of the facial nerve.

Eye drops may be required to prevent problems if you are unable to close your eye. Tape may also be used to close the eye while sleeping.

Read more about treatments for Bell’s palsy.

Complications

Around 3 in 10 people with Bell’s palsy will continue to experience weakness in their facial muscles, and 2 in 10 will be left with a more serious long-term problem.

Complications can include speech problems, reduced sense of taste and the permanent tensing of the facial muscles.

Read more about the complications of Bell’s palsy.

The Map of Medicine is used by doctors throughout the NHS to determine the best treatment options for their patients. NHS Choices offers everyone in England exclusive and free access to this cutting-edge internet resource, which lets you see exactly what your doctor sees.

The information in the Map has been approved by the UK’s leading clinical experts, is based on the best available clinical evidence, and is continually updated. To take advantage of this unique resource go to:

Map of Medicine: Bell’s palsy in adults

The symptoms of Bell’s palsy can vary, from a mild numbness of the face, to total paralysis.

The symptoms develop quickly and reach their peak within 48 hours. They include:

• weakness or paralysis in one side of the face, which may make it difficult to close the eyelid and cause the side of the mouth to droop
• irritation of the affected eye, such as dryness or increased tear production
• pain underneath the ear on the affected side of the face
• an altered or reduced sense of taste
• increased sensitivity to sound in the affected ear
• drooling from the mouth on the affected side of the face
• dryness of the mouth
• pain around the jaw
• headache
• ringing in one or both ears
• dizziness
• difficulty eating or drinking
• impaired speech

In most cases of Bell’s palsy, the symptoms will begin to improve within two to three weeks.

When to seek medical advice

As well as being a symptom of Bell’s palsy, facial weakness or paralysis can also be a sign of a more serious condition – such as a stroke.

Therefore, you should visit your nearest A&E department immediately or call 999 for an ambulance if you or someone you are with develops sudden facial paralysis so a doctor can determine the cause.

Most people recover fully from Bell’s palsy without treatment, but there are ways to accelerate the process and reduce the chance of complications.

Prednisolone is recommended as the most effective treatment for Bell’s palsy, and it should be started within 72 hours of the symptoms appearing.

Antiviral medications are not recommended as a treatment for Bell’s palsy.

Prednisolone

Prednisolone is a corticosteroid which works by helping to reduce inflammation (swelling), helping to speed up your recovery.

People with Bell’s palsy are usually advised to take prednisolone tablets twice a day for 10 days.

Possible side effects of prednisolone include:

• nausea (feeling sick)
• headache
• increased sweating
• indigestion
• increased appetite
• difficulty sleeping
• oral thrush
• dizziness

These side effects should improve within a few days as your body begins to get used to the medication.

Some people also experience mood changes, such as anxiety or depression, after taking steroids for a short period of time. You should visit your GP immediately if you experience mood changes, or if you have other side effects that are particularly troublesome.

Read more about the side effects of corticosteroids.

Speak to your GP before taking prednisolone if you are pregnant or breastfeeding.

Eye care

Tears play an important role in protecting your eyes and keeping them free of the dirt and bacteria that can cause eye infections.

If you have Bell’s palsy, you might find it difficult to close your eye, which can cause your tears to evaporate and leave your eye vulnerable to infection. So it’s very important to keep your eye lubricated.

Your GP may prescribe eye drops that contain ‘artificial tears’ for daytime use, plus an ointment that you should use at night. If you’re unable to shut your eye at night time, your GP will give you some surgical tape to close your eye.

If your eye symptoms get worse, you should visit the ophthalmology department of your local hospital for assessment.

Botulinum toxin injections

Botulinum toxin (Botox) injections can be used to treat either the affected or the unaffected side of the face in people with long-term Bell’s palsy.

Botox may be injected into the affected side of the face to relax any facial muscles that have become tight, or to reduce any unwanted muscle movements.

If the muscles in the unaffected side have become overactive or dominant, Botox may be injected into this side of the face to reduce muscle activity and balance the movement of the face.

Some of the long-term complications of Bell’s palsy can also be treated using Botox injections. These include:

• tears when eating
• eye-mouth synkinesias – where the facial nerve grows back in a different way, which can lead to a winking eye when eating, smiling or laughing

Read more about the complications of Bell’s palsy.

The Botox injections can help ease any discomfort that is experienced while eating and can also help to improve the overall appearance of the face. The injections need to be repeated every four months.

Further treatment

Most people with Bell’s palsy will make a full recovery within nine months. However, if you have not recovered by this time, there is a risk of more extensive nerve damage and further treatment may be needed.

Physiotherapy may be recommended. Your physiotherapist will teach you a series of facial exercises that will strengthen the muscles in your face to improve their co-ordination and range of movement.

Physiotherapy has been successful in a number of Bell’s palsy cases, although it may not be suitable or effective for everyone.

Plastic surgery is another possible option. The surgeon may not be able to restore nerve function, but may be able to improve the appearance and symmetry of your face.

Research has suggested that facial exercises, relaxation techniques and acupuncture can help speed up the recovery of Bell’s palsy and restore facial nerve function.