Cold sores — also called fever blisters — are fluid-filled lesions caused by herpes simplex virus type 1 infection.

What is it?

  • Cold sores — also called fever blisters — are fluid-filled lesions caused by herpes simplex virus type 1 infection.
  • If you've had a cold sore before, you may sense a new one coming by a telltale tingling on your lip. 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 are quite different from canker sores, another common condition people sometimes associate with cold sores. 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, which often precedes the blisters by one to two days
  • Usual duration of 10 to 14 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 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, although it's more typical for sores to appear within about one week of exposure. Sores usually clear up within about two weeks. The blisters form, break and ooze. Then a yellow crust forms and finally sloughs off to uncover pinkish skin that heals without a scar.


  • 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, as well as kissing, may spread herpes simplex virus type 1. In addition, oral-genital contact may cause a genital form of herpes simplex virus type 1 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, fatigue 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.


Cold sores are contagious. They can pass from one person to another through skin-to-skin contact. The greatest risk of infection is from the time the blisters appear until they have completely dried and crusted over. There is a possibility of spreading the virus for some time even after the skin has healed.

If you have a cold sore, avoid close contact with infants, anyone who has eczema (atopic dermatitis) or people with a suppressed immune system, such as people with cancer, AIDS or an organ transplant. These people are at higher risk of more severe infection.

Treatments and drugs

Cold sores generally clear up without treatment within about two weeks.

Topical treatments that may help relieve your symptoms include:

  • Lidocaine may provide short-term pain relief.
  • Benzocaine may protect cold sores from trauma and irritation.

Oral antiviral medications are available that may modestly shorten the duration of cold sores and decrease your pain, if started very early. These include:

Your doctor also may prescribe an antiviral medication to prevent a recurrence of cold sores, particularly if you:

  • Have very frequent bouts of cold sores
  • Experience significant, related illness during a cold sore outbreak
  • Have an identifiable trigger of cold sore recurrences — such as intense sunlight — and you anticipate exposure to that trigger

Lifestyle remedies

Cold sores generally clear up without treatment. In the meantime, the following steps may provide relief:

  • Use ointments. Over-the-counter (OTC) ointments, such as topical lidocaine or benzocaine, can help ease discomfort.
  • Take an OTC pain reliever. These include aspirin, paracetamol and ibuprofen. Aspirin has been linked with Reye's syndrome, so use caution when giving aspirin to children or teenagers. Though aspirin is approved for use in children older than age 2, children and teenagers recovering from chickenpox or flu-like symptoms should never take aspirin. Talk to your doctor if you have concerns.
  • Use cold or heat. Try applying ice or warm compresses to the blisters to ease the pain.
  • Let it heal. Avoid squeezing, pinching or picking at any blister.


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.
  • 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.