Cold sores, also known as herpes labialis, are caused by an infection with Herpes Simplex Virus I. Most people contract type I infections from family members and close friends during childhood. Patients develop symptoms 2 to 20 days after contact with an infected person. An outbreak is typically preceded by a tingling, burning, or itching sensation. After this “prodrome” small blisters or sores on or around the mouth develop. The sores typically heal within 2–3 weeks, but the herpes virus remains dormant in the facial nerves, following infection, periodically reactivating (in symptomatic people) to create sores in the same area of the mouth or face that was originally infected.

Cold sores have 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.

Anti-viral therapy may be prescribed to treat outbreaks as needed or patients may take a daily dose for suppression if they develop lesions frequently.