H erpes Simplex Virus or HSV is responsible for the most commonly occurring viral infections of the mouth and perioral soft tissues. Clinically, the characteristics findings of widespread vesicular eruptions into groups and gingival inflammation are evident. The vesicles affect any intraoral mucosa! surface and rupture to become ulcers, that rounded with red "halo" and very painful. Primary HSV infection refers to the first encounter between HSV and susceptible persons who are seronegative for HSV and, therefore, neutralizing antibodies and specific T-cell immunity against HSV are absent. Virus can be transmitted from infected to susceptible persons during close personal contact. During the infection, virion inoculates or gains entry to epithelial cells of the skin, lips, or mucosa. After infection, replicated viral DNA is encapsulated by new capsid proteins and the progeny bud through the nuclear membrane and are transported to the cell surface where lysis of the host cell releases infectious Herpes Simplex virions. Herpes Viruses possess the ability for reactivation of latent infection, and reactivation may result in asymptomatic shedding until resolved by the host immune response. HSV reactivation and cell-mediated control of HSV latency appears to be affected by a number of apparently unrelated stimuli that include emotional stress, menstruation, hormones, fever, ultraviolet radiation, immunosuppressions, etc.