Cold sores are caused by the herpes simplex virus (HSV) and are contagious. Because the virus is contagious, it is spread between people by kissing or other close physical contact .
Cold sores are caused by the herpes simplex virus (HSV) and are contagious. There are two types of herpes simplex virus: type I (mainly associated with cold sores or fever blisters) and type II (mainly genital). Cold sores are usually caused by the type I virus. Because the virus is contagious, it is spread between people by kissing or other close physical contact . Contact with infected saliva and genital secretions can also spread the virus. You are most contagious when you have an active blister-like sore. Once the blister has dried and crusted-over, the risk of contagion is reduced. However, a person infected with HSV can pass it on to another person even if a cold sore is not present because the virus can still be transmitted in saliva.
Despite the popular myth, it is highly unlikely to catch herpes (cold sores) from contaminated surfaces, towels or washcloths. After the first infection, the virus enters the nerve cells that supply sensation to the skin and travels up the nerve until it comes to a place called a 'ganglion'. There it lays dormant. Sometimes the virus can begin to multiply and cause an attack or outbreak again and travels down the nerve to the skin where it multiplies, thus causing the cold sore. It is not fully understood exactly how this happens, but we do know that certain conditions are associated with recurrences: