Snapshot A 19-year-old woman with no significant past medical history presents to her primary care clinic with a blister on her outer lip, which started yesterday. She recalls a more severe prior episode about 1 year ago. She is sexually active with men and uses condoms for contraception. She denies any recent illness or sore throat. On physical exam, a cluster of erythematous, crusting vesicles are present along the oral commissure. Introduction Infection of the oral mucous membrane by Herpes Simplex Virus (HSV) typically HSV-1 but also HSV-2 Primary infections seen mainly in children fever, systemic illness Following primary infection the virus is latent in the trigeminal ganglia reactivation following sunlight exposure, stress Highly contagious transmitted via mucous membranes Presentation Primary HSV fever, lymphadenopathy red, swollen, and painful vesicles typically on lips, gums, palate, and tongue known as herpetic gingivostomatitis Recurrent HSV classically described as "grouped vesicles on an erythematous base," which eventually crust over typically on vermillion border of lips (see figure) or mucosa of hard palate known as herpetic labialis can be preceded by prodrome of itching, tingling or burning Diagnosis Usually clinical based on appearance If non-specific, can perform viral culture and PCR of an unroofed vesicle Management Oral medication acyclovir or valacyclovir Topical, less effective than oral medication acyclovir, penciclovir, docosanol cream