Bell’s palsy is a condition that causes sudden weakness in the muscles on one side of the face. Often the weakness is short-term and improves over weeks. The weakness makes half of the face appear to droop. Smiles are one-sided, and the eye on the affected side is hard to close.Bell’s palsy also is known as acute peripheral facial palsy of unknown cause. It can occur at any age. The exact cause is not known. Experts think it’s caused by swelling and irritation of the nerve that controls the muscles on one side of the face. Bell’s palsy could be caused by a reaction that occurs after a viral infection.Symptoms usually start to improve within a few weeks, with complete recovery in about six months. A small number of people continue to have some Bell’s palsy symptoms for life. Rarely, Bell’s palsy occurs more than once.