Bell's palsy is the most common cause of facial paralysis. It usually affects just one side of the face. Symptoms appear suddenly and are at their worst about 48 hours after they start. They can range from mild to severe and include

• Twitching
• Weakness
• Paralysis
• Drooping eyelid or corner of mouth
• Drooling
• Dry eye or mouth
• Excessive tearing in the eye
• Impaired ability to taste

Scientists think that a viral infection makes the facial nerve swell or become inflamed. You are most likely to get Bell's palsy if you are pregnant, diabetic or sick with a cold or flu.

Three out of four patients improve without treatment. With or without treatment, most people begin to get better within 2 weeks and recover completely within 3 to 6 months.

Bell's palsy is a neurological disorder that causes paralysis or weakness on one side of the face. One of the nerves that controls muscles in your face becomes injured or stops working properly.

Symptoms include:

• Sudden weakness or paralysis on one side of your face
• A drooping eyebrow and mouth
• Drooling from one side of your mouth
• Difficulty closing an eyelid, which causes eye dryness

Most often these symptoms lead to significant facial distortions.

People living with Bell's palsy may also develop:

• Facial pain or abnormal sensations
• Excessive tearing in one eye
• Problems with taste
• Low tolerance for loud noises
• Pain around the jaw and behind the ear
• Problems eating or drinking

Symptoms appear suddenly over a 48- to 72-hour period and generally start to improve with or without treatment after a few weeks. They vary from person to person and can be mild to severe. Usually, you will recover some or all facial function within a few weeks to six months. Sometimes the facial weakness may last longer or be permanent.

Bell's palsy is the most common cause of facial paralysis, although its exact cause is unknown. It results from dysfunction of cranial nerve VII, which connects your brain to the muscles that control facial expression (the nerve also is involved with taste and ear sensation). In rare cases, Bell's palsy can affect both sides of your face.

Bell's palsy is estimated to affect about 40,000 people in the United States every year. It can affect anyone of any gender and age but seems to be highest in those in people 15 to 45 years old. Risk factors for Bell's palsy include pregnancy, preeclampsia, obesity, hypertension, diabetes, and upper respiratory ailments.

Possible triggers of Bell's palsy may include:

• An existing (dormant) viral infection
• Impaired immunity from stress, sleep deprivation, physical trauma, minor illness, or autoimmune syndromes
• Infection of a facial nerve and resulting inflammation
• Damage to the myelin sheath (fatty covering that insulates nerve fibers)

Bell's palsy occurs when the nerve that controls the facial muscles, the 7th cranial nerve, is swollen, inflamed, or compressed, resulting in facial weakness or paralysis. Exactly what causes this damage is unknown.

Many scientists believe that a viral infection such as viral meningitis or the common cold sore virus -- herpes simplex-- causes the disorder when the facial nerve swells and becomes inflamed in reaction to the infection. The disorder has also been associated with influenza or a flu-like illness, headaches, chronic middle ear infection, high blood pressure, diabetes, sarcoidosis, tumors, Lyme disease, and trauma such as skull fracture or facial injury. There may also be an inherited tendency toward developing Bell's palsy.

Because the facial nerve has so many functions and is so complex, damage to the nerve or a disruption in its function can lead to many problems. Symptoms of Bell's palsy, which vary from person to person and range in severity from mild weakness to total paralysis, may include twitching, weakness, or paralysis on one or both sides of the face, drooping of the eyelid and corner of the mouth, drooling, dryness of the eye or mouth, impairment of taste, and excessive tearing in one eye. Most often these symptoms, which usually begin suddenly and reach their peak within 48 hours, lead to significant facial distortion.

Other symptoms may include pain or discomfort around the jaw and behind the ear, ringing in one or both ears, headache, loss of taste, hypersensitivity to sound on the affected side, impaired speech, dizziness, and difficulty eating or drinking.

A doctor will examine you for any upper and lower facial muscle weakness on one side of your face (including the forehead, eyelid, and mouth) that began in less than 72 hours. During the exam, the doctor will rule out other possible causes of facial paralysis. There is no specific laboratory test to confirm diagnosis of the disorder.

Routine laboratory or imaging studies are not necessary for most cases, but sometimes they can help to confirm your diagnosis or rule out other diseases or conditions that can cause facial weakness (e.g., brain tumor, stroke, myasthenia gravis, and Lyme disease). If no specific cause can be identified, the condition can be diagnosed as Bell's palsy.

Tests for Bell's palsy may include:

• Electromyography (EMG), which uses thin wire electrodes that are inserted into a muscle to assess changes in electrical activity during movement and when the muscle is at rest. EMGs can confirm the presence of nerve damage and determine the severity and the extent of nerve involvement.
• Blood tests can sometimes help diagnose other concurrent problems such as diabetes and certain infections.
• Diagnostic imaging such as magnetic resonance imaging (MRI) or computed tomography (CT) scans can rule out other structural causes of pressure on the facial nerve (e.g., an artery compressing the nerve) and also check the other nerves.

Medications

• Your doctor might prescribe steroids if you have new-onset Bell's palsy. In most instances, oral steroids should be started within 72 hours of symptom onset if possible, to reduce inflammation and swelling and increase the probability of recovering facial nerve function. Some people with Bell's palsy or facial weakness with co-existing conditions may not respond well to or be able to take steroids.
• Antiviral agents (in addition to steroids) might increase the probability of recovery of facial function, although their benefit has not been clearly established.
• Analgesics such as aspirin, acetaminophen, or ibuprofen may relieve pain. Because of possible drug interactions, individuals taking prescription medicines should always talk to their doctors before taking any over-the-counter (OTC) drugs.

Eye protection

• Keeping your eyes moist and protecting them from debris and injury, especially at night, is important. Lubricating eye drops, such as artificial tears or eye ointments or gels, and eye patches also are effective.

Other therapies

• Physical therapy, facial massage, or acupuncture may provide a small improvement with facial nerve function and pain. Electrical stimulation of the facial nerve may improve.

Surgery

• On rare occasions, cosmetic or reconstructive surgery may be needed to correct some damage such as an eyelid that will not fully close or a crooked smile.