Robert B. Heiman, Leading Formulator for Skin & Health Care for 40 YearsCold Sore Research by Mayo Clinic

The scenario is all too familiar: You feel a tingling on your lip and a small, hard spot that you can't yet see. Sure enough, in a day or two, red blisters appear on your lip. It's another cold sore, probably happening at a bad time, and there's no way to hide it or make it go away quickly.

Cold sores — also called fever blisters — are quite different from canker sores, a condition people sometimes associate with cold sores.

Cold sores are common. Though you can't cure or prevent cold sores, you can take steps to reduce their frequency and to limit the duration of an occurrence.

Cold sore symptoms include:

  • Small, painful, fluid-filled blisters on a raised, red area of your skin, typically around the mouth
  • Pain or tingling, called the prodrome, often precedes the blisters by one to two days
  • Usual duration of seven to 10 days

Cold sores most commonly appear on your lips. Occasionally, they occur on your nostrils, chin or fingers. And, although it's unusual, they may occur inside your mouth — more often on your gums or hard palate, which is the roof of your mouth. Sores appearing on other soft tissues inside your mouth, such as the inside of the cheek or the undersurface of the tongue, may be canker sores but aren't usually cold sores.

Signs and symptoms may not start for as long as 20 days after exposure to the herpes simplex virus, and usually last seven to 10 days. The blisters form, break and ooze. Then a yellow crust forms and finally sloughs off to uncover pinkish skin that heals without a scar.

Causes

By Mayo Clinic staff

Certain 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.

Treatments and drugs

By Mayo Clinic staff

Cold sores generally clear up without treatment in seven to 10 days. Topical symptomatic treatments such as topical lidocaine or benzyl alcohol (Zilactin) may help relieve symptoms.

Using an antiviral medication may modestly shorten the duration of cold sores and decrease your pain, if started very early. If you experience very frequent bouts, your doctor may prescribe an antiviral medication as a cold sore treatment or to prevent cold sores.

Prevention

By Mayo Clinic staff

You can take steps to guard against cold sores, to prevent spreading them to other parts of your body or to avoid passing them along to another person. Cold sore prevention involves the following:

  • Avoid kissing and skin contact with people while blisters are present. The virus can spread easily as long as there are moist secretions from your blisters. In persons with depressed immune systems, the virus can be spread even after the skin appears to be healed.
  • Avoid sharing items. Utensils, towels, lip balm and other items can spread the virus when blisters are present.
  • Keep your hands clean. Wash your hands carefully before touching another person when you have a cold sore.
  • Be careful about touching other parts of your body. Your eyes and genital area may be particularly susceptible to spread of the virus.
  • Avoid triggers. If possible try to avoid or prevent conditions that stress your body, such as getting a cold or the flu, not getting enough sleep or staying in the sun for long periods of time without applying sunblock.
  • Use sunblock. Apply sunblock to your lips and face before prolonged exposure to the sun — during both the winter and the summer — to help prevent cold sores.