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What You Need to Know

Cold sores are proof that life can be unfair: Some people get them, others don't. Besides being itchy and painful, cold sores (also called fever blisters) make you feel self-conscious. Some treatments can cut short the symptoms when used at the first sign of an outbreak. Other treatments can relieve symptoms. Use this pictorial guide to learn how to recognize, prevent, and treat cold sores.

Don't Blame Your Cold

Cold sores aren't caused by the common cold. They're caused by the herpes simplex virus (HSV), passed on through contact with infected skin or body fluids. There are two types of HSV, type 1 and type 2. Cold sores are usually caused by type 1. HSV-1 damages the skin as it reproduces, creating cold sores that last about a week. Between outbreaks, HSV-1 hides inside nerve cells, so it's never completely cured.

Who Gets Cold Sores and Why

More than half of us have been infected with the HSV-1 virus, usually from 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. One study identified six genes that many cold sore sufferers share. Three of those genes may relate to how HSV-1 reactivates itself, causing outbreaks.

Stress Can Trigger a Cold Sore

HSV-1 spends most of its time inactive, hiding in nerves. Many people have familiar triggers that tend to bring HSV-1 out of seclusion, causing cold sores. Sunlight, fever, stress, and menstruation are common triggers. Some people get cold sores twice a year; for others, it's a frustrating, stressful, monthly ritual.

Canker Sores Aren't the Same

Cold sores usually appear on the lip; canker sores affect the inside of the mouth. Canker sores aren't caused by the herpes virus and aren't contagious. No one knows what causes them. Cold sores generally start with red, irritated skin. Blisters form, break open, and crust over before healing.

When You're Contagious

A cold sore is caused by skin damage as the herpes virus reproduces inside infected cells. From the time skin turns itchy or red, HSV-1 is likely present and can be spread. Cold sores are most contagious when blisters are present and just after they break open, until the skin is completely healed and looks normal again. But some people can transmit the virus through their saliva at any time, even if they never get cold sores.

How Is the Cold Sore Virus Spread?

HSV spreads through body fluids. The cold sore virus is usually present on an infected person's lip, even if there's no obvious sore. Kisssing is the main way it is transmitted. Because HSV-1 can also live in saliva, sharing kitchen utensils or drinking glasses can also spread it. Oral sex can lead to HSV-1 infection of the partner's genitals.

How to Avoid Spreading the Virus

Use caution while you have a cold sore: no kissing; no sharing of toothbrushes, silverware, or glasses; and no oral sex. That will reduce most of the spread of HSV-1.

Easing Cold Sore Pain

While the first outbreak can last up to 2 weeks, recurrent outbreaks usually last about 1 week. Some people may find relief with hot or cold compresses. There is no cure for cold sores, but some over-the-counter creams and gels can help with burning and pain.

Antiviral Creams

Antiviral creams can reduce the time it takes a cold sore to heal if applied at the first sign of a cold sore. Docosanol cream (Abreva) is available over the counter. Acyclovir (Zovirax) cream and penciclovir (Denavir) cream are available by prescription.

Prescription Cold Sore Medications

Oral antiviral prescription medications can also reduce the amount of healing time when taken at the first sign of a cold sore -- red or itchy skin, for example. Acyclovir is begun before cold sores fully flare and taken 5 times daily. Another one, a single-dose acyclovir tablet (Sitavig), is put directly on your gums and releases medicine as it dissolves. Valacyclovir (Valtrex) is taken at the first sign of a cold sore and then 12 hours later. Famciclovir (Famvir) is taken as a single dose.

Is This a Cold Sore?

What about a cold sore that's not on your lip? They are not as common, but cold sores can appear anywhere on the face, including on the cheek, chin, or nose. Most people's cold sores reappear in the same area each time.

Can You Spread It on Your Body?

It's possible, though rare, to spread the cold sore virus from one part of the body to another. It can happen by touching a cold sore, then touching an area of broken skin or a mucous membrane, the moist protective lining of skin found in areas like the eyes or vagina. That can lead to a herpes skin infection. You can prevent this self-spread -- or autoinoculation -- by washing your hands and not touching the cold sore.

When Herpes Infects the Eye

Other areas the cold sore virus can infect are the finger (herpetic whitlow) and the eye (ocular herpes). Ocular herpes most often happens on the cornea. It is the most common infectious cause of corneal blindness in the U.S. Quick treatment is needed to prevent eye damage. Herpetic whitlow is painful. When kids get herpetic whitlow, it's usually because they've spread the virus from a cold sore by finger- or thumb-sucking.

Preventing Outbreaks

It can be tough to prevent cold sores, but reducing your triggers can help. Stay out of the sun or use sunscreen and UV-blocking lip balm. Learn and practice stress management strategies that work for you. Keep your immune system healthy by getting plenty of sleep and daily exercise.

When to See a Doctor

If you have severe or frequent cold sore outbreaks, see your doctor.

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Reviewed by Stephanie S. Gardner, MD on October 26, 2015