Bell's palsy is a sudden facial paralysis that usually strikes all or part of one side of the face. Men or women of any age can suffer Bell's palsy. Your risk of experiencing Bell's palsy in your lifetime is about 1 in 60. Few people are struck by Bell's palsy more than once in their lives.

Bell's palsy can be a frightening experience, appearing suddenly with symptoms that cause many people to think they're having a Stroke. In reality, stroke symptoms are quite different, and Bell's palsy is a comparatively harmless condition that usually clears up without treatment.

The exact cause of Bell's palsy is unknown, but most researchers believe that the most likely cause is a viral infection (herpes simplex or herpes zoster virus) that causes swelling and inflammation of the facial nerve. Although research has found that the herpes simplex 1 virus (the virus that causes Cold Sores) is present, in many cases a direct link to the virus has not been proven.

Herpes zoster, the virus that causes Shingles and Chickenpox, hides in your nerve roots. Many experts believe this virus is responsible for some cases of Bell's palsy, but this theory is still disputed.

Some people are more prone to Bell's palsy than others. Your risk is higher if you have one of these conditions:

• a common cold or some other upper respiratory ailment
• cold sores
• Diabetes
• Influenza
• pregnancy (particularly the third trimester)

Bell's palsy usually appears suddenly, often overnight. The primary symptom is weakness and paralysis on one side of the face. You may find that you can't make the same expressions as usual. Typically, you'll be unable to fully close one eye. Other possible symptoms include:

• altered sense of taste
• facial pain, pain in or behind the ear (in fewer than 50% of cases)
• no tears in one eye
• sensitivity to noise on the affected side
• numbness or heaviness in the face

Stroke is associated with other symptoms such as a severe headache, severe dizziness, difficulty speaking, numbness or weakness in the arms or legs, and blurred vision. With Bell's palsy you may have some trouble talking, but it's purely muscular, and is not caused by bleeding or a blood clot in the brain. Other conditions that can cause facial paralysis include Ramsay Hunt syndrome, Lyme Disease, and brain tumour.

Usually, the symptoms appear at once. Occasionally, they worsen over a few days. Steady, progressive paralysis over several weeks is not a sign of Bell's palsy.

The most serious complication seen in Bell's palsy is permanent mild facial paralysis. This is found in a minority of cases. Overall, about 80% recover completely over weeks to months, and most of the rest improve.

Another complication is increased risk of stroke. Stroke prevention and follow-up is recommended.

Some people don't recover completely. This is more likely in people who are older than 60 or who are experiencing weakness or paralysis on both sides of the face.

People who don't recover completely may be left with one or more of the following symptoms:

• abnormal blink
• asymmetrical smile
• buccinator paralysis (food caught in cheek of paralyzed side)
• corneal damage
• drooling of liquids from corner of paralyzed mouth
• dry eye
• excessive perspiration
• frozen muscle in the nostril area
• hyperacusis (perceiving sounds as unusually loud)
• impaired taste
• impaired speech
• synkinesis (involuntary movement associated with a voluntary movement)

Bell's palsy is diagnosed based on its symptoms and physical signs. There are no specific tests to diagnose Bell's palsy, but your doctor will perform a thorough physical examination and may order certain tests (e.g., blood tests) to rule out other medical conditions that can cause facial paralysis. Additional tests such as CT scans or MRI scans are usually not necessary, but may be used to rule out other medical causes of facial paralysis.

Bell's palsy must be differentiated from Lyme disease, Guillain-Barré syndrome, sarcoidosis, parotid tumor, and stroke. Lymphoma can also in rare instances be a cause of facial paralysis.