Cold sores are lesions on the skin, typically around the mouth and nose, caused by a herpes simplex virus, and commonly affect about 20 percent of the adult population. They generally last seven to eight days, and about a quarter of those people who get them have three or more episodes a year. For people with the virus, cold sores may be triggered by a variety of factors, including exposure to the sun, stress, a cold, fever or menstruation.

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