Facial nerve paralysis: Loss of voluntary movement of the muscles on one side of the face due to abnormal function of the facial nerve (also known as the 7th cranial nerve) which supplies those muscles. Facial nerve paralysis is also called Bell's palsy.

The cause of facial nerve paralysis is often not known, but is thought to be due to a virus.

The disease typically starts suddenly and causes paralysis of the muscles of the side of the face on which the facial nerve is affected.

Treatment is directed toward protecting the eye on the affected side from dryness during sleep. Massage of affected muscles can reduce soreness. Sometimes prednisone is given to reduce inflammation during the first weeks of illness.

The prognosis (outlook) with Bell's palsy is generally good. About 80% of patients recover within weeks to months. Conversely, about 20% of patients do less well. The condition was originally described in 1830 by the Scottish anatomist and neurologist Sir Charles Bell (1774- 1842). The word "palsy" is a corruption (and contracture) of the French word "paralysie" which means "paralysis."