Cold sores around the lips & mouth, due to infection with the Herpes simplex virus. The Herpes simplex viruses are regarded as being the most common human virus parasites. Two types have been distinguished. Type 1 (HSV-1) infection used to associated with most oral & central nervous infections, with Type 2 (HSV-2) involved in genital herpes infections. This distinction is no longer clear-cut, due to a supposed increase in oral sexual activities. HSV-1 infection commonly occurs in childhood. After the primary infection, the virus persists in a latent state to re-appear & cause recurrent cold sores.