Herpes simplex virus type 1 (HSV-1) and, to a lesser extent, type 2 (HSV-2) are the aetiological agents of recrudescent herpes labialis (RHL). The available literature on patterns of HSV-1 shedding into the oral cavity at the prodromal stage of disease, during recrudescences and also during asymptomatic periods, is reviewed, as are the potential sources of virus and the known trigger factors leading to viral reactivation. Attention is given to the methodologies in use for the detection of HSV-1 and the relevance to the risk of cross-infection in surgery. This review also discusses the increase in incidence of HSV-1 genital infections and the significance of salivary inhibitors of the herpes simplex type 1 virus.