Definition of Bell's palsy:

Bell's palsy is a disorder of the nerve that controls movement of the muscles in the face.

Damage to this nerve causes weakness or paralysis of these muscles. Paralysis means that you cannot use the muscles at all.

Causes, incidence, and risk factors:

Bell's palsy affects about 30,000 - 40,000 people a year in the United States.

Bell's palsy involves damage to the seventh cranial (facial) nerve. This nerve controls the movement of the muscles of the face.

Bell's palsy is thought to be due to swelling (inflammation) of this nerve in the area where it travels through the bones of the skull.

The cause is often not clear. A type of herpes infection called herpes zoster might be involved. Other conditions that may cause Bell's palsy include:

• HIV infection
• Lyme disease
• Middle ear infection
• Sarcoidosis