Herpes labialis, or orolabial herpes,[1]:368 is an infection of the lip by herpes simplex virus (HSV-1). An outbreak typically causes small blisters or sores on or around the mouth commonly known as cold sores or fever blisters. The sores typically heal within 2–3 weeks, but the herpes virus remains dormant in the facial nerves, following orofacial infection, periodically reactivating (in symptomatic people) to create sores in the same area of the mouth or face at the site of the original infection.

HSV-1 affected 57.7% of Americans tested in a 1999-2004 study.[2] By age 50, 80%–90% of adults have the virus.[3] More than 50 million adults in the U.S. develop symptomatic episodes every year.[4] Cold sore has a rate of frequency that varies from rare episodes to 12 or more recurrences per year. People with the condition typically experience one to three attacks annually. The frequency and severity of outbreaks generally decreases over time.[5]

The virus is transmitted from cold sores and also when there are no symptoms, as it can make copies of itself on the skin in the absence of a blister.