Adam's lip had been feeling itchy all day — itchy and a little tingly, like someone was tickling it lightly. When he woke up the next morning and his lip still felt strange, he looked in the mirror and yelled "What's on my mouth?" His mom took a look and said, "Oh, you have a cold sore."

What's that? Adam wondered.

What Is a Cold Sore?

A cold sore is a small blister that is reddish or purple. They are usually on the outer edge of the lip, on just one side. Cold sores can appear one at a time or in little bunches, and they are sometimes filled with fluid. They usually crust over and form a scab before they go away. They last a week or 2 and usually don't require any special treatment.

Although they're called cold sores, you don't need to have a cold to get one. Some people call them fever blisters, but you don't have to have a fever to have one, either. (Cold sores aren't the same as canker sores, which are small white sores that are always found inside the mouth.)

What Causes Cold Sores?

Cold sores are caused by a virus called herpes (say: hur-peez). Herpes is one of the most common viral infections in the world. The medical name for the specific virus that causes cold sores is herpes simplex.

There are two types of herpes simplex infection: herpes simplex virus one (called HSV-1 for short) and herpes simplex virus two (called HSV-2 for short). Although both can cause cold sores around a person's mouth, most are caused by HSV-1.

HSV-1 is so common that most Americans get infected with it, although many never have any symptoms. People can catch HSV-1 by kissing a person with a cold sore or sharing a drinking glass or utensils, so it's easy to see why there are so many cold sores around.

Kids who get infected with HSV-1 may get cold sores occasionally for the rest of their lives. That's because even after the sores themselves dry up and go away, the virus stays in the body, waiting around for another time to come out and cause more sores. When a cold sore reappears, it is often in the same place as the previous one.

How Can I Keep From Getting Cold Sores?

Although HSV-1 isn't a big deal, it's a good idea to try to keep cold sores as far away as possible. If someone you know has a cold sore, don't kiss him or her and don't drink out of the same glass or use the same knife, fork, or spoon. Sharing towels, washcloths, or napkins is off-limits, too, because the virus may survive on the fabric.

If you've had cold sores before, it can be hard to tell what might make them come back. For some kids, too much stress, too much time in the sun, or getting sick can cause cold sores to reappear. Eating well, getting enough rest, and learning how to deal with stress are important things for any kid to do, especially a kid who is likely to get cold sores. Putting on sunblock lip balm and sunscreen on the face before going out in the sun may help prevent cold sores from reappearing in kids who tend to get them.

Treating Cold Sores

For most kids, the sores go away on their own without any special treatment from a doctor. If you get a cold sore, try holding some ice wrapped in cloth on the sore. It also might help to eat a popsicle.

Sometimes, if the cold sores are making a kid sick, a doctor may prescribe a special medicine that fights the herpes simplex virus. Some kids may take acetaminophen or ibuprofen if their sores are painful.

While you're waiting for the cold sore to go away, wash your hands regularly and don't pick at it. You'll only get in the way of your body's natural healing process. Picking at a cold sore is also bad news because it's easy to spread the virus to other parts or your body, like your fingers or eyes. Worse yet, you might spread the virus to other people. No one will thank you for giving them a cold sore!

Reviewed by: Steven Dowshen, MD
Date reviewed: October 2010