Herpes simplex is a common and usually mild infection. It can cause "cold sores" or "fever blisters" on the mouth or face--what is called oral herpes. It can also cause similar symptoms in the genital area, which is known as genital herpes.

A virus causes herpes--either herpes simplex type 1 (HSV-1) or herpes simplex type 2 (HSV-2). It is different from other common viral infections because once it is introduced it lives in the body over a lifetime, often without symptoms or with periodic symptoms. This is called "latency.". The virus can travel the nerve pathways in a part of the body and hide away, sleeping, in the nerve roots for long periods of time. Even though HSV may not cause "cold sores" or genital signs or symptoms at the moment, it can still cause symptoms later.