(1) Herpes simplex type 1: A herpes virus that causes cold sores and fever blisters in and around the mouth. In rare cases, as when someone's immune system is severely compromised, this virus can cause infection of the brain (encephalitis).
Herpes simplex type 1 is also known as human herpesvirus 1 (HHV-1).
Common Misspellings: herpies simplex type 1
(2) There are two types of herpes simplex viruses (HSV). HSV type 2 is the one that most commonly causes genital herpes. You can get HSV type 2 during sexual contact with someone who has a genital HSV-2 infection. The infection causes painful sores on the genitals in both men and women. HSV type 1 is the herpes virus that is usually responsible for cold sores of the mouth, the so-called “fever blisters.” You get HSV-1 by coming into contact with the saliva of an infected person.
However, HSV type 1 can cause genital herpes, usually caused by oral-genital sexual contact with a person who has the oral HSV-1 infection, and HSV type 2 can cause cold sores.
In the United States, one out of five of the total adolescent and adult population are infected with herpes simplex virus.