RELATED STORIES • Bell's palsy: Will local anesthetic worsen it?

Note: All links within content go to MayoClinic.com

Bell's palsy is a weakness or paralysis of the muscles that control expression on one side of your face. The disorder results from damage to one of a pair of facial nerves that runs beneath each ear to the muscles in your face.

The condition may result in a droopy appearance of your face. This can be a blow to your self-esteem, but most often Bell's palsy isn't serious.

The problem can occur at any age. Bell's palsy occurs more often in pregnant women, in people with diabetes or upper respiratory ailments, such as the flu or a cold, and in people with conditions that compromise their immune systems. Also called facial palsy, Bell's palsy is named for Dr. Charles Bell, a 19th-century surgeon from Scotland who first described the condition.

Bell's palsy clears up on its own within weeks or months for most people. In some cases, doctors prescribe a corticosteroid medication within the first few days, hoping to increase the likelihood of a good recovery.

Signs and symptoms of Bell's palsy may include:

• Sudden onset of paralysis or weakness on one side of your face, making it difficult to smile or close your eye on the affected side
• Facial droop and difficulty with facial expressions
• Facial stiffness or a feeling that your face is being pulled to one side
• Pain behind or in front of your ear on the affected side
• Sounds that seem louder on the affected side
• Pain, usually in the ear on the affected side
• Headache
• Loss of taste on the front portion of your tongue
• Changes in the amount of tears and saliva your body produces

The severity of Bell's palsy can range from mild weakness to total paralysis on one side of your face. The onset of the problem is fairly abrupt, generally becoming apparent within several hours to a day or two. You may notice symptoms when you awaken. Pain in the vicinity of the ear can precede the palsy by a day or two. Weakness or paralysis usually peaks within 48 hours after onset of signs and symptoms. The faster the signs and symptoms progress, the more serious the weakness or paralysis you'll experience.

Each facial nerve controls all muscles on one side of your face, except for muscles involved in chewing. The cause of Bell's palsy is still unclear, and its development isn't well understood. But many scientists believe that a viral infection — perhaps most commonly by the herpes simplex virus, the same virus that causes cold sores — can cause the facial nerve to become swollen and injured. Impairment of electrical impulses directed to your facial muscles by the damaged nerve results in the weakness or paralysis of these muscles.

Most people with Bell's palsy recover completely within a few months, with or without medical treatment. For a few people, Bell's palsy can be severe or involve complications.

Not all instances of facial paralysis or weakness are due to Bell's palsy. See your doctor if you experience facial weakness, drooping or paralysis to determine the underlying cause and severity of the illness.

Your doctor may be able to make a preliminary diagnosis of Bell's palsy by looking at your face and asking you to try to move your facial muscles. Other conditions, such as a stroke, infections and tumors, also may cause facial muscle weakness, mimicking Bell's palsy.

If after a few days there's still doubt about the diagnosis, your doctor may recommend other tests:

• Electromyography (EMG). This test can confirm the presence of nerve damage and determine its severity. An EMG can measure the electrical activity of a muscle in response to stimulation and the nature and speed of the conduction of electrical impulses along a nerve.
• Brain imaging. This kind of test isn't always necessary, but a test such as magnetic resonance imaging (MRI) or computed tomography (CT) may be needed on occasion to eliminate possible sources of pressure on the facial nerve, such as an infection, tumor or skull fracture.

Although a mild case of Bell's palsy normally disappears within a month, recovery from a case involving total paralysis varies. If the damage to your facial nerve is unusually severe, the fibers may be irreversibly damaged. Another complication can arise from misdirected regrowth of nerve fibers, which can result in involuntary contraction of certain muscles when you're trying to move others (synkinesis). For example, when you smile, the eye on the affected side may close.

Doctors aren't sure that any treatment changes the ultimate outcome of Bell's palsy in most people. Most recover fully with or without treatment.

Courses of treatment may include:

• Anti-inflammatory medication. A short course of prescription corticosteroid medication, such as prednisone, may reduce inflammation and swelling in the narrow, bony channel through which the facial nerve travels.
• Antiviral medication. Prescription antiviral medications, such as acyclovir (Zovirax) and famciclovir (Famvir), may limit or reduce damage to the nerve from some viral causes.
• Massage. Facial massage may help prevent permanent contractures of the paralyzed muscles before recovery takes place.

You'll need to protect your eye from damage to its outer layer (cornea) because of the absence of blinking on the side of your face with weakness. An excessively dry eye can result in clouding of the cornea and lead to a corneal ulcer, which can interfere with vision. You can protect your eye with artificial tears (a special eye lubricant generally used at night), an eye patch or a transparent eye shield attached to your face with tape.

Acetaminophen, ibuprofen or aspirin may help to ease pain. You might also try applying moist heat to the affected side of your face.