Carol Miller, age 10, of North Las Vegas, Nev., for her question:

WHAT CAUSES A COLD SORE?

A cold sore is a skin infection that usually appears around the mouth. The sore is caused by a virus.

Technically called a herpes simplex, a cold sore is a disease that may appear anywhere on the body. It may be started by a fever, a cold or even by a sunburn.

When the infection develops about the lips, it is called a cold sore or a fever blister. The sore starts as a patch of redness that tingles and burns. Small yellowish blisters form in the area and then they run together, break, ooze and make a crust.

Most cold sores last from two to three weeks. No medicine will heal it, but a mild nonirritating salve will ease the discomfort.