Herpes is a sexually transmitted disease (STD) caused by the herpes simplex virus (HSV). HSV-type 1 commonly causes mouth or lip sores that resemble fever blisters (oral herpes). HSV-type 2 typically affects the genital area (genital herpes). The HSV virus cannot be removed from the body once infected but may cause no symptoms for prolonged periods (it may remain dormant). When dormant, the virus typically lives within the nerve cells. The sores of HSV may return when a person is experiencing emotional or physical stress or immune suppression. However, attacks of herpes may recur for no identifiable reason.