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The Basics

Cold sores -- you might hear them called fever blisters -- are proof that life can be unfair. Some people get them, others don’t. If you get them, don't worry. There are ways to treat and prevent them.

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Your Cold Isn't to Blame

Despite the name, that isn’t what causes them. The herpes simplex virus type 1 (HSV-1) is most often the cause. You get it from contact with an infected person’s skin or body fluids. The virus damages your skin as it reproduces. That leaves behind weepy sores that last about a week. Between outbreaks, HSV-1 hides inside nerve cells, so it’s never completely cured.

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Why Doesn't Everyone Get Them?

About two-thirds of us have been infected with the HSV-1 virus. It usually comes via well-meaning kisses from relatives or romantic partners. So why do only an unlucky few get cold sores? The answer may be in your genes. Most of the people who get cold sores share genes that may relate to how HSV-1 acts in your body. This could be what causes outbreaks.

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What Are Your Triggers?

HSV-1 lives in your nerves. It’s pretty quiet most of the time, but you may have triggers that bring it out of hiding and cause cold sores. They can range from sunlight or a fever to stress and getting your period. Some people get cold sores twice a year or less. For others, it’s a monthly ordeal.

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Canker Sores Aren't the Same

Cold sores usually appear on your lip. Canker sores affect the inside of your mouth. They don’t involve the herpes virus and aren’t contagious. No one knows what causes them. Cold sores generally signal their arrival with a warning period of red, irritated skin. Blisters form, burst, and then crust over before they heal.

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When Are You Contagious?

From the time your skin turns itchy or red, the virus is likely present and you can spread it. You’re most contagious when blisters show up and just after they burst. Once your skin is completely healed and looks normal again, you can’t spread it that way. But you can still pass the virus through your saliva at any time, even when you don't have a cold sore.

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How Does the Virus Spread?

Through body fluids. It’s usually present on an infected person’s lip, even if there’s no obvious sore. Kisses are the main method. Because the virus often lives in saliva, you can also spread it if you share kitchen utensils or drinking glasses. Oral sex sometimes leads to infection of your partner's genitals.

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Can You Stop the Spread?

Yes. Use caution while you have a sore. Don’t kiss, and don't share toothbrushes, silverware, or glasses. Skip oral sex. That will reduce most of the spread of HSV-1, although you may not be able to control the spread completely.

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How to Ease Your Pain

While the first outbreak can last up to 2 weeks, the ones after that may not be longer than a week. There’s no cure for cold sores, but some over-the-counter creams and gels can ease symptoms like burning and pain. You can also try hot or cold compresses. 

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Antiviral Creams Can Help

They often shorten the time it takes a cold sore to heal. But they work best if you put them on at the very first sign of an outbreak. Docosanol cream is available over the counter. Acyclovir (Zovirax) cream and penciclovir (Denavir) cream are available by prescription.

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Prescription Meds Are Available

They can lower the amount of healing time when you take them at the first sign of a cold sore -- like tingly, red, or itchy skin. You’ll start acyclovir before cold sores fully flare and take it five times a day for 5 days, or you can take valacyclovir (Valtrex) at the first sign of a cold sore and then 12 hours later. Famciclovir (Famvir) can be given as a single dose of medicine. So can acyclovir buccal (Sitavig), but instead of swallowing it you place against your gums and it releases the medicine as it dissolves.

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How Do You Know It's a Cold Sore?

What about a cold sore that isn’t on your lip? They aren’t as common, but they can pop up anywhere on your face, like your cheek, chin, or nose. Most people’s cold sores reappear in the same area each time.

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Can It Spread to Your Body?

Yes, but it’s rare. It can happen if you touch a cold sore, then touch an area of broken skin or a mucous membrane (that’s the moist, protective lining found in places where your body opens to the outside -- mouth, nose, genitals). That can lead to a herpes skin infection. To prevent this, wash your hands and don’t touch the cold sore.

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Where Else Might It Strike?

Your eyes: This is called ocular herpes, and it most often affects the cornea. It’s the leading infectious cause of corneal blindness in the U.S., so get treatment as soon as possible. Herpetic whitlow is a painful condition that affects your fingers. Kids often get it when they have a cold sore and suck their fingers or thumb.

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How Do You Prevent Outbreaks?

It’s tough to hold them off entirely, but there are things you can do to help keep them at bay. Learn what your triggers are and avoid them. Stay out of the sun, or use sunscreen and UV-blocking lip balm. Figure out what works to manage your stress. Keep your immune system healthy with plenty of sleep and daily exercise.

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When Should You See a Doctor?

Make an appointment if:

  • You have a weakened immune system.
  • The cold sores don't heal within 2 weeks.
  • Your symptoms are severe.
  • Your eyes are irritated.
  • You have severe or frequent cold sore outbreaks.
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Sources | Medically Reviewed on 11/09/2019 Reviewed by Nayana Ambardekar, MD on November 09, 2019


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American Academy of Dermatology: "Viral Infections: Herpes Simplex."

University of Illinois at Chicago, Department of Ophthalmology and Visual Sciences: "Ocular Herpes Simplex."

Cernik, C. Archives of Internal Medicine, June 9, 2008.

American Dental Association: "Canker Sores and Cold Sores."

Kriesel, J. Human Genome Variation, published online Nov. 20, 2014.

National Eye Institute: "Facts About the Cornea and Corneal Disease."

Xu, F. JAMA, 2006.

Corey, L. New England Journal of Medicine, 1986.

Pope. L.E. Antiviral Research, 1998.

Spruance, S.L. New England Journal of Medicine, 1977.

UpToDate: Treatment of herpes simplex virus type 1 infection in immunocompetent patients.”

Merriam Webster: “Mucous Membrane.”

Mayo Clinic: “Cold Sore: Symptoms.”

Reviewed by Nayana Ambardekar, MD on November 09, 2019

This tool does not provide medical advice. See additional information.

THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional medical advice, diagnosis or treatment and should not be relied on to make decisions about your health. Never ignore professional medical advice in seeking treatment because of something you have read on the WebMD Site. If you think you may have a medical emergency, immediately call your doctor or dial 911.