Definition of Herpes labialis:

Herpes labialis is an infection caused by the herpes simplex virus. It leads to the development of small and usually painful blisters on the skin of the lips, mouth, gums, or lip area. These blisters are commonly called cold sores or fever blisters.

Causes, incidence, and risk factors:

Herpes labialis is a common disease caused by infection of the mouth area with herpes simplex virus type 1. Most people in the United States are infected with the type 1 virus by the age of 20

The initial infection may cause no symptoms or mouth ulcers. The virus remains in the nerve tissue of the face. In some people, the virus reactivates and produces recurrent cold sores that are usually in the same area, but are not serious. Herpes virus type 2 usually causes genital herpes and infection of babies at birth (to infected mothers), but may also cause herpes labialis.

Herpes viruses are contagious. Contact may occur directly, or through contact with infected razors, towels, dishes, and other shared articles. Occasionally, oral-to-genital contact may spread oral herpes to the genitals (and vice versa). For this reason, people with active herpes lesions on or around the mouths or on the genitals should avoid oral sex.

The first symptoms usually appear within 1 or 2 weeks -- and as late as 3 weeks -- after contact with an infected person. The lesions of herpes labialis usually last for 7 to 10 days, then begin to resolve. The virus may become latent, residing in the nerve cells, with recurrence at or near the original site.

Recurrence is usually milder. It may be triggered by menstruation, sun exposure, illness with fever, stress, or other unknown causes.