Bell's palsy is paralysis of the facial nerve of unknown cause. The diagnosis is made when no other cause can be identified. Bell's palsy is thought to be caused by a viral infection of the facial nerve. The most likely virus is the herpes simplex virus. Other names for this condition are "idiopathic facial palsy" or Antoni's palsy.

Bell's palsy is usually a self-limiting, non-lifethreatening condition that spontaneously remits (gets better by itself) within six weeks. The incidence is 15 to 40 new cases per 100,000 people per year. It's about three times more common during pregnancy and slightly more common in menstruating females. In general, it becomes more common with age.

The typical symptoms of Bell's palsy include:

• Unilateral acute paralysis of facial muscles. The paralysis involves all muscles, including the forehead.
• About half the time, there is numbness or pain in the ear, face, neck or tongue.
• There is a preceding viral illness in 60% of patients.
• There is a family history of Bell's palsy in 10% of patients.
• Less than 1% of patients have bilateral problems.
• There may be a change in hearing sensitivity (often increased sensitivity).

The proposed mechanism of injury of the facial nerve in Bell's palsy is:

• Primary viral infection (herpes) sometime in the past.
• The virus lives in the nerve (trigeminal ganglion) for a time that can range from months to years.
• The virus becomes reactivated at a later date.
• The virus reproduces and travels along the nerve.
• The virus infects the cells surrounding the nerve (Schwann cells), resulting in inflammation.
• The immune system responds to the damaged Schwann cells, which causes inflammation of the nerve and subsequent weakness or paralysis of the face.

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