Bell's palsy is a form of temporary facial paralysis resulting from damage or trauma to one of the two facial nerves. It is the most common cause of facial paralysis. Generally, Bell's palsy affects only one of the paired facial nerves and one side of the face, however, in rare cases, it can affect both sides. Symptoms of Bell's palsy usually begin suddenly and reach their peak within 48 hours. Symptoms range in severity from mild weakness to total paralysis and may include twitching, weakness, or paralysis, drooping eyelid or corner of the mouth, drooling, dry eye or mouth, impairment of taste, and excessive tearing in the eye. Bell?s palsy often causes significant facial distortion. Most scientists believe that a viral infection such as viral meningitis or the common cold sore virus -- herpes simplex-- causes the disorder when the facial nerve swells and becomes inflamed in reaction to the infection.