Bell's palsy is a sudden weakness and paralysis on one side of the face due to injury to the facial nerve. It occurs in approximately 40,000 Americans each year. It affects men and women equally.

The exact cause of Bell's palsy is unknown. It is suspected that an irritated facial nerve becomes swollen. As the facial nerve passes through narrow openings in the skull, it is compressed and symptoms result.

Doctors believe a herpes virus may cause the nerve to become inflamed, and, in turn, cause Bell’s palsy. Lyme disease or other infections may also be a cause of facial weakness.

Paralysis of the facial nerve may also be caused by:

• Head or facial injuries
• Tumors
• Cancer or infection in the cerebrospinal fluid (CSF)
• Strokes
• Abscess
• HIV
• Infection
• Autoimmune disease
• Drug therapy, such as chemotherapy
• Hereditary diseases
• Other conditions that cause paralysis of the facial nerve

These factors increase your chance of developing Bell's palsy. Tell your doctor if you have any of these risk factors:

• Family members who have Bell's palsy
• Pregnancy
• Diabetes
• Cold or flu
• Weakened immune system
• HIV infection
• Smoking
• Hypertension
• Ear infection
• Head or facial trauma
• Cancer history

Bell's palsy symptoms may come on suddenly or develop over a few days. Initial symptoms may include:

• Pain behind the ear that precedes the weakness and paralysis
• Ringing sound in the ears
• Slight fever
• Slight hearing impairment
• Slight increase in sensitivity to sound on the affected side.

Symptoms of full-blown Bell's palsy may include:

• Facial weakness or paralysis:
  • Usually on one side
  • Forehead is smooth
  • Not able to smile
• Numbness just before the weakness starts
• Drooping corner of the mouth
• Drooling
• Decreased tearing
• Inability to close an eye, which can lead to:
  • The eye becoming red and dry
  • Ulcers forming on the cornea
  • Infection
  • Possible loss of the eye
• Impaired taste
• Sound sensitivity in one ear
• Earache
• Slurred speech

Late complications (occurring 3-4 months after onset) can include:

• Contracture of the facial muscles
• Tearing from eye during eating

The doctor will ask about your symptoms and medical history, and do a physical exam.

Other tests may include:

• Hearing test—to see if nerve damage involves the hearing nerve, inner ear, or hearing mechanism
• Balance test—to see if balance nerves are involved
• Lumbar puncture —a test of the cerebrospinal fluid (CSF) from the lower back; to rule out meningitis , autoimmune disorders, or cancer spreading from a tumor
• Tear test—measures the eye's ability to produce tears
• CT scan —a type of x-ray that uses a computer to make pictures of structures inside the head to see if there is an infection, tumor, bone fracture , or other problem in the area of the facial nerve
• MRI scan —a test that uses magnetic waves to make pictures of structures inside the head to see if there is an infection, tumor, bone fracture, or other problem in the area of the facial nerve
• Electrical test—to determine damage to the facial nerve
• Blood tests—to check for diabetes, HIV infection, or Lyme disease

In most cases, symptoms go away within a few weeks without treatment. Many cases of Bell's palsy completely resolve after a few months.

Protecting the eye is important. This is because you may not be able to blink. If an underlying cause of the symptoms is known, it is treated. In some cases, however, symptoms may never go away.

Below are several ways to treat Bell's palsy:

Your doctor may prescribe corticosteroids. These reduce swelling and pain. For example, studies have shown that prednisolone can improve the chance of complete recovery from Bell's palsy.

In addition to corticosteroids, antiviral medications (eg, valacyclovir [Valtrex], acyclovir [Zovirax]) may also be prescribed for this condition. But, the evidence is mixed as to how effective antivirals are in treating Bell's palsy.

Some doctors try to surgically relieve pressure on the nerve by removing part of the bone. This is an unproven procedure. It is considered controversial and is no longer commonly done. If the eyelid will not close, other surgeries around the eye may be considered.

You may need to apply lubricant or put drops in the eye. The eye can be covered and taped closed at night. Do not place tape directly on the eyelid. An eye patch may be worn to keep the eye closed. This helps moisten and keep particles out of the eye. Massage of the weakened facial muscles may be beneficial.

Symptoms can be very distressing. You may need help dealing with emotional issues associated with the condition.

Physical therapy and speech therapy may be helpful in improving symptoms.

If you are diagnosed with Bell's palsy, follow your doctor's instructions .