Most cold sores are caused by type 1 herpes simplex virus (HSV-1).[1] HSV-1 infections are extremely common, with an estimated 38% of American children and 64% of adults having antibodies against HSV-1.[2] HSV-1 is commonly acquired in childhood through nonsexual contact, but it can also be picked up in adulthood through sexual or nonsexual contact.[3] Cold sores can sometimes be caused by type 2 herpes simplex (HSV-2), although this is less common.[1] Roughly 16% of American adults have antibodies against HSV-2.[4]
Even though most people who have had an initial HSV infection don’t get cold sores, by some estimates, about 30% of Americans have recurrent cold sore outbreaks.[5]