what exactly is a cold sore?

Cold sores are small, painful, fluid-filled blisters or sores that appear on the lips, mouth, or nose that are caused by a virus. The sores can be painful and usually last a few days. Unlike most viral infections, the cold sore virus is not completely eliminated by the body defenses. For this reason, cold sores often recur.

The virus that causes cold sores is known as the herpes simplex virus (HSV). There are two types of HSV, type I and type II. Cold sores are usually caused by type I. Herpes simplex infections are contagious. The virus is spread from person to person by kissing or other close contact with sores or even from contact with apparently normal skin that is shedding the virus. Infected saliva is also a means of transmitting the virus. People are most contagious when they have active blister-like sores. Once the blisters have dried and crusted over (within a few days), the risk of contagion is significantly lessened. However, a person infected with HSV can pass it on to another person even when a cold sore is not present. This is because the virus is sometimes shed in saliva even when sores are not present. Despite popular myth, it is almost impossible to catch herpes (cold sores) from contaminated surfaces, towels, or washcloths.