DefinitionHerpes simplex is a viral infection that mainly affects the mouth or genital area.Causes, incidence, and risk factorsThere are two strains of herpes simplex viruses:Herpes simplex virus type 1 (HSV-1) is usually associated with infections of the lips, mouth, and face. It is the most common herpes simplex virus and many people develop it in childhood. HSV-1 often causes sores (lesions) inside the mouth, such as cold sores (fever blisters), or infection of the eye (especially the conjunctiva and cornea). It can also lead to infection of the lining of the brain (meningoencephalitis). It is transmitted by contact with infected saliva. By adulthood, 30 - 90% of people will have antibodies to HSV-1. The likelihood of childhood infection is higher among those with lower socioeconomic st