Herpes simplex- is a viral disease from the herpesviridae family caused by both Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2). Infection with the herpes virus is categorized into one of several distinct disorders based on the site of infection. Oral herpes, the visible symptoms of which are colloquially called cold sores or fever blisters, is an infection of the face or mouth. Oral herpes is the most common form of infection. Genital herpes, known simply as herpes, is the second most common form of herpes. Other disorders such as herpetic whitlow, herpes gladiatorum, ocular herpes, cerebral herpes infection encephalitis, Mollaret's meningitis, neonatal herpes, and possibly Bell's palsy are all caused by herpes simplex viruses.

Herpes viruses cycle between periods of active disease—presenting as blisters containing infectious virus particles—that last 2–21 days, followed by a remission period. Genital herpes, however, is often asymptomatic, though viral shedding may still occur. After initial infection, the viruses are transported along sensory nerves to the sensory nerve cell bodies, where they become latent and reside lifelong. Causes of recurrence are uncertain, though some potential triggers have been identified, including immunosuppressant drugs. The previously latent virus then multiplies new virus particles in the nerve cell and these are transported along the axon of each neuron to the nerve terminals in the skin, where they are released. Over time, episodes of active disease reduce in frequency and severity.