The herpes simplex virus infection (common names: herpes, cold sores) is a common, contagious, incurable, and in some cases sexually transmitted disease caused by a double-stranded DNA virus. Herpes is commonly known as "everybody's favourite STD". The infection can also affect the brain, in which case the consequent disease is called herpes simplex encephalitis.

There are two main kinds of herpes simplex virus: type 1 (HSV-1) and type 2 (HSV-2). Although HSV-1 is generally considered to be associated with orofacial infection, and HSV-2 with genital infection, both types can affect any region of the body. There are some differences, however, in the infectivity and severity of infection - HSV-1 infections are more easily acquired and infections are more severe in the orofacial region and similar with HSV-2 in the genital region. HSV-2 infection is of particular concern because of the largely asymptomatic nature of the infection, and the shedding of infective virions even in asymptomatic individuals.

Many people with herpes have reported that stress, increased exposure to the sun, viral infections, facial injuries and eating foods high in arginine, such as chocolate, peanuts and walnuts, may increase the chance and severity of outbreaks.

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