Signs and symptoms of Bell's palsy come on suddenly and may include:

• Rapid onset of mild weakness to total paralysis on one side of your face — occurring within hours to days
• Facial droop and difficulty making facial expressions, such as closing your eye or smiling
• Drooling
• Pain around the jaw or in or behind your ear on the affected side
• Increased sensitivity to sound on the affected side
• Headache
• A decrease in your ability to taste
• Changes in the amount of tears and saliva you produce

In rare cases, Bell's palsy can affect the nerves on both sides of your face.

Although the exact reason Bell's palsy occurs isn't clear, it's often related to exposure to a viral infection. Viruses that have been linked to Bell's palsy include the virus that causes:

• Cold sores and genital herpes (herpes simplex)
• Chickenpox and shingles (herpes zoster)
• Infectious mononucleosis (Epstein-Barr)
• Cytomegalovirus infections
• Respiratory illnesses (adenovirus)
• German measles (rubella)
• Mumps (mumps virus)
• Flu (influenza B)
• Hand-foot-and-mouth disease (coxsackievirus)

The nerve that controls your facial muscles passes through a narrow corridor of bone on its way to your face. In Bell's palsy, that nerve becomes inflamed and swollen — usually related to a viral infection. Besides facial muscles, the nerve affects tears, saliva, taste and a small bone in the middle of your ear.

Bell's palsy occurs more often in people who:

• Are pregnant, especially during the third trimester, or who are in the first week after giving birth
• Have an upper respiratory infection, such as the flu or a cold
• Have diabetes

Recurrent attacks of Bell's palsy are rare. But in some of these cases, there's a family history of recurrent attacks — suggesting a possible genetic predisposition to Bell's palsy.

A mild case of Bell's palsy normally disappears within a month. Recovery from a more severe case involving total paralysis varies. Complications may include:

• Irreversible damage to your facial nerve
• Abnormal regrowth of nerve fibers, resulting 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
• Partial or complete blindness of the eye that won't close due to excessive dryness and scratching of the clear protective covering of the eye (cornea)