Understanding cold sores - the basics

What are cold sores?

Cold sores -- also called fever blisters -- are a painful infection caused by the herpes simplex virus (HSV). These sores are usually caused by HSV Type 1 but can less commonly be due to HSV Type 2.�They may show up anywhere on your body but are most likely to appear on your gums, the outside of your mouth and lips, your nose, cheeks or fingers. Blisters form, then break and ooze; a yellow crust develops and eventually sloughs off, revealing new skin underneath. The sores usually last 7 to 10 days and are contagious until they crust over completely.

90% of all people get at least one cold sore in their lives. This first occurrence is often the worst. Some children who are affected may become seriously ill. After the first infection, many people develop antibodies and never have another cold sore.

Although cold sores are generally not serious, the infection may be life-threatening for anyone who has AIDS or whose immune system is suppressed by other disorders or medications.

The infection from a cold sore may cause blindness if it spreads to the eye and meningitis or encephalitis if it spreads to the brain.

What causes cold sores?

Cold sores are usually caused by the herpes simplex virus (HSV)-Type 1, which is transmitted by such forms of contact as kissing an infected person or sharing eating utensils, towels or razors. Genital herpes is usually caused by herpes simplex virus Type 2. A person with a cold sore who performs oral sex on another person can give that person genital lesions with HSV-1 and similarly, genital herpes lesions can be spread to the lips.

Sores may develop as late as 20 days after exposure to the virus. Once the virus enters your body, it may emerge years later at or near the original site of entry. About two days before an attack you may experience itching or sensitivity at the site. The virus may be triggered by certain foods, stress, fever, colds, allergies, sunburn and menstruation.