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Mouth & Teeth

Canker Sores

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What’s a Canker Sore?

If you’ve ever had those open, shallow sores in your mouth and taken a gulp of orange juice, you know what a pain canker sores can be. Canker sores are fairly common: About 1 in 5 people get them on a regular basis. The good news is, they usually go away on their own without treatment.

Canker sores (also known as aphthous ulcers) only happen inside the mouth. You can get them on or under the tongue and on the inside of the cheeks and lips — the parts of the mouth that can move. They usually pop up alone, but sometimes they show up in small clusters.


Signs It’s a Canker Sore

Your mouth might tingle or burn before a canker sore appears. Soon, a small red bump rises. Then after a day or so it bursts, leaving an open, shallow white or yellowish wound with a red border. The sores are often painful and can be up to half an inch across, although most of them are much smaller. A person who has canker sores doesn’t usually have the fever or swollen lymph nodes that can show up with some other kinds of sores. Aside from the annoying pain in the mouth, you’ll generally feel OK.

The good news is that canker sores are not contagious like some other mouth sores, such as cold sores. You can’t get canker sores by sharing food or kissing someone.

If you have a sore and you’re wondering if it’s a cold sore or a canker sore, just look at where it shows up: Cold sores usually appear outside the mouth, around the lips, chin, or nostrils. Canker sores are always found inside the mouth.

You can also get spots in your mouth when you have an infection like chickenpox or measles. In some cases of these diseases, the rash actually spreads into the mouth. If you have chickenpox or measles, you’ll find spots on other parts of your body as well, so you’ll know they’re not canker sores.


Canker sores usually begin showing up between the ages of 10 and 20, although they can happen at any time in a person’s life. No one knows exactly what causes them. One thing that doctors have noticed is that although the sores are not contagious, they can run in families. That means if your parents or siblings get canker sores, the genes you share with them make it more likely that you’ll develop the sores, too.

There may be a connection between canker sores and stress. If you get canker sores around exam time or some other big event in your life, it may be a sign of how much stress you’re under. In addition, about twice as many women as men get them. Doctors think that may be due to the differences in male and female hormones, especially because women often get them during certain times in their menstrual cycle.

Some research suggests that using products containing sodium lauryl sulfate (SLS) can be associated with canker sores. SLS is a foaming agent found in most toothpastes and mouthwashes. Finally, not getting the right nutrition, such as not getting enough iron or vitamin B12, may also contribute to some cases of canker sores.

What You Can Do

Most canker sores will heal on their own in a few days to a couple of weeks. While you’re waiting for them to disappear, you can take over-the-counter pain relievers like ibuprofen or acetaminophen for the pain. You’ll also want to watch what you eat. Spicy foods and acidic foods such as lemons or tomatoes can be extremely painful on these open wounds. Stay away from hard, scratchy, or crunchy foods like nuts, toast, pretzels, or potato chips for a while. They can poke or rub the sore.

Be careful when you brush your teeth. Brush and rinse with toothpastes and mouthwashes that don’t contain sodium lauryl sulfate. And avoid brushing the sore itself with a toothbrush, which will make it worse.

There are lots of “home remedies” for canker sores out there, but no evidence to show that they help sores heal faster. If you have canker sores that do not get better after a few weeks, if the sores keep coming back, or if they make you feel so sick that you don’t want to eat, call your doctor or dentist. He or she may prescribe a topical medicine or special mouthwash to help heal the sores.

For medications that are applied directly to the sore, first blot the area dry with a tissue. Use a cotton swab to apply a small amount of the medication, and do not eat or drink for at least 30 minutes to make sure that the medicine is not immediately washed away.

In some cases, doctors may want to do blood tests to find out if another condition — such as a vitamin deficiency, a problem with your immune system, or even a food allergy — could be contributing to the sores.

Although they can certainly be a pain, in most cases canker sores aren’t serious and should go away on their own.

Reviewed by: Elana Pearl Ben-Joseph, MD
Date reviewed: January 2013