Cold sores, also commonly known as fever blisters, are caused by an infection with the herpes simplex 1 (HSV- 1) virus. Almost everyone has been exposed to the HSV-1 virus (an estimated 95% of all people), and the infection causes one or more fluid-filled blisters in the tissues of the mouth or around the nose. After the initial outbreak, the virus lies dormant in the skin and surrounding nerve tissue, and is reactivated from time to time, most often due to colds, influenza, too much sun, or stress. Why the virus causes outbreaks at different times is not completely understood. At the time of outbreaks, the fluid within the blisters and the skin around the ulcer contain high levels of the HSV-1 virus, and so are highly contagious until the ulcer is healed. Frequent handwashing and avoiding direct contact with others will minimize the risk of spreading HSV-1. Some antiviral medications may shorten the course of the cold sore if given early in the outbreak.
Editor's note: Infrequently, HSV-1 is also responsible for eye infections and other skin infections. A small percentage of genital herpes cases are also caused by HSV-1. More information about cold sores is found in the article about their causative agent, the herpes simplex 1 virus.
See AlsoHerpes Simplex 1 Virus.