Cold Sores
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Cold Sores

(Fever Blisters; Herpes Labialis; Herpes Stomatitis; Canker Sore)

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Cold sores are small, painful, fluid-filled blisters, usually on the lips or gums.

Herpes Simplex on the Lips

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Cold sores are usually caused by the herpes simplex 1 virus. It can sometimes be caused by the herpes 2 virus that causes genital herpes . The two viruses are related, but different. The virus invades the skin, then lies dormant for weeks or months before causing inflammation and blistering.

In most cases, people contract the virus as infants or young children. The first episode of illness with herpes simplex 1 virus causes a systemic illness. Then the virus lies dormant until it is reactivated. This results in painful cold sores. They are usually located at the border of the colored part of the lip.

The virus can be spread by:

  • Contact with the fluid from a cold sore of another person, or sores of genital herpes in most cases of the herpes 2 virus
  • Contact with the eating utensils, razors, towels, or other personal items of a person with active cold sores
  • Sharing food or drink with a person with active cold sores
  • Contact with the saliva of a person who has the herpes simplex virus

Risk Factors

Infection with this virus is so common that everyone is considered at risk.

Once the herpes simplex 1 virus is present in the body, the following risk factors can trigger cold sores to form:

  • Transplantation
  • Malnutrition
  • Infection, fever, cold, or other illness
  • Exposure to sun
  • Physical or emotional stress
  • Certain foods or drugs
  • Weakened immune system
  • Menstruation
  • Eczema
  • Physical injury or trauma
  • Dental or other oral surgery
  • Excessive exercise

Cold sores often form without an identifiable trigger.


The first episode of herpes simplex 1 infection may result in 3-14 days of:

  • Swollen, sore throat
  • Mouth sores
  • Fever
  • Decreased energy
  • Aches and pains
  • Difficulty eating
  • Swollen glands in the neck
  • Headache

In the day just prior to the virus reappearing as a cold sore, you may notice some itching, burning, or pain in the area where the cold sore will appear.

Symptoms of cold sores on the lips, mouth, or skin include:

  • Small, painful, fluid-filled, red-rimmed blisters
  • Pain, tingling, or itching for a day or two before the blister appears
  • After a few days, drying of the blister, which then forms a yellow crust and shallow ulcers


The doctor will ask about your symptoms and medical history, and examine the blisters. Usually, the doctor can easily diagnose a cold sore by looking at it. Cold sores have a relatively classic appearance. In rare cases, the doctor may need to take a piece of a blister to analyze it or take a blood sample for testing.


Cold sores will usually heal within 7-20 days. Treatments for blisters on the lips, mouth, or skin include:

  • Putting ice on blisters to lessen pain and promote healing
  • Not rubbing or scratching blisters
  • Nonprescription pain relief drugs to lessen pain and discomfort
  • Nonprescription cold sore/fever blister cremes and ointments to lessen pain
  • Antibiotic drugs if the blister becomes infected by bacteria
  • Antiviral cream or ointment, although the evidence for its effectiveness is not strong
  • Oral antiviral medications may be given the moment you feel a cold sore coming on or could be taken on a regular basis to suppress frequent outbreaks. To decrease discomfort and help cold sores go away more quickly, you may be given one of the following:
    • Zovirax (acyclovir)
    • Valacyclovir (Valtrex)
    • Famciclovir ( Famvir)


To prevent the oral spread of the herpes simplex 1 or 2 virus:

  • Avoid skin contact, kissing, or sharing food, drink, or personal items with people who have active cold sores
  • Avoid performing oral sex on a person with active genital herpes
  • If you have an active cold sore, avoid touching the infected area (to avoid spreading the virus to other people and/or other parts of your body)

To prevent recurring outbreaks of cold sores or blisters:

  • Avoid long periods of time in the sun.
  • Use sun block on lips and face when in the sun.
  • Get adequate rest and relaxation to minimize stress.


American Academy of Dermatology


Canadian Family Physician


Arduino PG, Porter SR. Oral and perioral herpes simplex virus type 1(HSV-1) infection: review of its management. Oral Diseases. 2006;12:254-270.

Beers MH. The Merck Manual of Medical Information . 2nd ed. Whitehouse Station, NJ: Merck Research Laboratories; 2003.

Cold sore. website. Available at: . Accessed October 7, 2005.

Emmert DH. Treatment of common cutaneous herpes simplex virus infections. Am Fam Physician . 2000;61:1697.

Groves MJ. Transmission of herpes simplex virus via oral sex. Am Fam Physician. 2006;1;73:1153; discussion 1153.

Herpes simplex. American Academy of Dermatology website. Available at: . Accessed July 15, 2008.

Schmid-Wendtner MH, Korting HC. Penciclovir cream—improved topical treatment for herpes simplex infections. Skin Pharmacol Physiol. 2004;17:214-8.

Spruance S, Bodsworth N, Resnick H, et al. Single-dose, patient-initiated famciclovir: a randomized, double-blind, placebo-controlled trial for episodic treatment of herpetic labialis. J Am Acad Dermatol . 2006;55:47-53.

Spruance SL, Jones TM, Blatter MM, Vargas-Cortes M, et al. High-dose, short-duration, early valacyclovir therapy for episodic treatment of cold sores: results of two randomized, placebo-controlled, multicenter studies. Antimicrobial Agent Chem . 2003;1072-1080.

Last reviewed December 2007 by Ross Zeltser, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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