Herpes labialis is infection of the lips, mouth, or gums with the herpes simplex virus. It leads to the development of small, painful blisters commonly called cold sores or fever blisters.

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 this virus by age 20.

The initial infection may cause no symptoms or mouth ulcers. The virus then remains dormant (asleep) 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, which usually causes genital herpes and can infect babies during birth to infected mothers, can also cause herpes labialis.

Herpes viruses are contagious. Spread may occur through intimate and personal contact, 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).