Nothing is more vexing than a cold sore that appears right on the edge of your lip for all to see. Yet you don't feel much better when they crop up inside your mouth. They hurt and are difficult to treat.

Once a cold sore strikes, it tends to return again and again. This is because the virus herpes simplex I that usually causes cold sores can go underground after the initial attack and lurk in the body for months or years, triggering sporadic flare-ups. Menstrual periods, fevers, colds, dental work, eczema, sun exposure, and stress can trigger repeat performances.

The first visible sign of a cold sore is usually a cluster of small fluid-filled blisters that form a red ring. As the blisters heal, they dry up, and usually disappear within two weeks.

You can take steps to either prevent or treat cold sores. For prevention:

• Do your best to manage emotional and physical stress.
  
• Limit exposure to the sun. (Apply zinc oxide or a sun block to lips or other susceptible
  areas if you expect to spend time outdoors.)
  
• Avoid contact with anyone who has an active cold sore.
  
• Wash your hands frequently while the virus is active, to prevent it from spreading.
• To relieve cold sores:
• Apply ice for 1 hour within a day of the sore's first appearance. Drink cool beverages to
  soothe the pain.
  
• Don't scratch or pick at the sore.
  
• Take a nonprescription pain reliever like aspirin or acetaminophen to relieve cold sore pain.
  
• If the sore is severe, your doctor may prescribe a medication called acyclovir (brand name Zovirax) to both treat and prevent cold sores.