Cold sores are caused by a contagious virus called herpes simplex. There are two types of herpes simplex virus. Type 1 usually causes oral herpes, or cold sores. Type 1 herpes virus infects more than half of the U.S. population by the time they reach their 20s. Type 2 usually affects the genital area

Some people have no symptoms from the infection. But others develop painful and unsightly cold sores that last for a week or more. Cold sores usually occur outside the mouth -- on the lips, chin, and cheeks, or in the nostrils. When they do occur inside the mouth, it is usually on the gums or the roof of the mouth.

There is no cure for cold sores. Medicines can relieve some of the pain and discomfort associated with the sores. These include ointments that numb the blisters, antibiotics that control secondary bacterial infections, and ointments that soften the crusts of the sores.