Herpes simplex virus 1 and 2 (HSV-1 and HSV-2) are two strains of the herpesvirus family, Herpesviridae, which cause infections in humans. HSV-1 and 2 are also referred to as Human Herpes Virus 1 and 2 (HHV-1 and HHV-2).
After an initial, or primary, infection, HSV establishes latency, during which the virus is present in the cell bodies of nerves which innervate the area of original outbreak. During reactivation, the virus is produced in the cell and transported outwardly via the nerve cell's axon to the skin. The ability of HSV to become latent leads to the chronic nature of Herpes infection; after the initial infection subsides, Herpes symptoms may periodically recur in the form of outbreaks of herpetic sores near the site of original infection.
Herpes infections are marked by painful, watery blisters in the skin or mucous membranes (such as the mouth or lips) or on the genitals. The blisters resemble those seen in chickenpox — an infection caused by a third member of the alpha-Herpesviridae subfamily, Varicella Zoster Virus (VZV), also known as Human Herpes Virus 3 (HHV-3). Lesions heal with a crudescent scab, the hallmark of herpetic disease. Herpes is contagious if the carrier is producing and releasing ("shedding") virus. This is particularly likely during an outbreak, although individuals may shed virus between outbreaks. Although no cure is yet available, treatments exist which reduce the likelihood of viral shedding. An HSV infection on the lips is commonly known as a "cold sore" or "fever blister" and should not to be confused with a canker sore; canker sores are not caused by the HSV virus.