Bell's palsy is a condition that causes sudden weakness in the muscles on one side of the face. In most cases, the weakness is temporary and significantly improves over weeks. The weakness makes half of the face appear to droop. Smiles are one-sided, and the eye on the affected side resists closing.
Bell's palsy, also called facial palsy, is a disorder caused by damage to the facial nerve, the nerve that supplies the muscles of the face. This damage causes partial or total paralysis of one side of the face.
No one is certain why Bell's palsy occurs, but it may be due to a virus such as herpes simplex, the "cold sore" virus. About 1 of 70 people develop Bell's palsy, usually just once.