Bell's palsy is a temporary form of facial paralysis. It results from damage to the nerve that controls movement of the muscles in the face.

Bell's palsy is a form of cranial mononeuropathy VII, and it is the most common type of this nerve damage. Bell's palsy affects about 2 in 10,000 people.

Bell's palsy involves damage to the seventh cranial (facial) nerve. This nerve controls the movement of the muscles of the face. The cause is often not clear, although herpes infections may be involved.

Bell's palsy is thought to be linked to inflammation of the nerve in the area where it travels through the bones of the skull. Other conditions, such as sarcoidosis, diabetes, and Lyme disease, are associated with Bell's palsy.

Symptoms usually start suddenly, and range from mild to severe. They may include:

• Twitching in face
• Weakness in face
• Face feels stiff or pulled to one side
• Droopy eyelid or corner of mouth
• Drooling due to inability to control facial muscles
• Facial paralysis of one side of the face, makes it hard to close one eye
• Change in facial expression (for example, grimacing)
• Dry eye or mouth
• Loss of sense of taste
• Difficulty with eating and drinking
• Pain behind or in front of the ear, may occur 1-2 days before muscle weakness
• Sensitivity to sound (hyperacusis) on the side of the face affected
• Headache

Examination shows weakness in the upper and lower part of the face, usually on just one side. Weakness may affect the forehead, eyelid, or mouth. Blood pressure is normal.

Blood tests for sarcoidosis or Lyme disease may be considered. If there is no improvement in the facial paralysis after several weeks, an MRI is done to rule out other causes.

An EMG and nerve conduction studies may also be done to determine the severity of nerve damage.

Other causes of cranial mononeuropathy VII, such as head injury and tumor, need to be ruled out.