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Causes
By Mayo Clinic staffCertain strains of the herpes virus cause cold sores. Herpes simplex virus type 1 usually causes cold sores. Herpes simplex virus type 2 is usually responsible for genital herpes. However, either type of the virus can cause sores in the facial area or on the genitals. You get the first episode of herpes infection from another person who has an active lesion. Shared eating utensils, razors and towels may spread this infection.
Once you've had an episode of herpes infection, the virus lies dormant in the nerve cells in your skin and may emerge again as an active infection at or near the original site. You may experience an itch or heightened sensitivity at the site preceding each attack. Fever, menstruation, stress and exposure to the sun may trigger a recurrence.
Cold sores and canker sores
Cold sores are quite different from canker sores, which people sometimes associate with cold sores. Cold sores are caused by reactivation of the herpes simplex virus, and they're contagious. Canker sores, which aren't contagious, are ulcers that occur in the soft tissues inside your mouth, places where cold sores don't typically occur.
