Bell's palsy is a form of facial paralysis resulting from a dysfunction of the seventh cranial nerve (the facial nerve), which results in the inability to control facial muscles on the affected side.  Several conditions can cause facial paralysis such as a brain tumor, stroke, and Lyme disease.  However, if no specific cause can be identified, the condition is knows as Bell's palsy.

Bell's palsy is usually self-limiting.  The hallmark of this condition is a rapid onset of partial or complete palsy that often occurs overnight.  In rare cases (<1%) it can occur bilaterally resulting in total facial paralysis.  It is thought that an inflammatory condition leads to swelling of the facial nerve.  The nerve travels through the skull in a narrow bone canal beneath the ear.  Nerve swelling and compression in the narrow bone canal are thought to lead to nerve inhibition, damage or death.  No readily identifiable cause for Bell's palsy has been found.

In either situation, a thorough medical history and physical examination are the first steps in making a diagnosis and beginning the proper treatment.