Canker Sores

What Is a Canker Sore?

If you've ever had those open, shallow sores in your mouth and taken a gulp of orange juice — ouch! — you know what a pain canker sores can be. You're not alone, either. About one in five people get recurrent canker sores. So what can you do about them? Read on to find out.

Canker sores, also known as aphthous ulcers, are small sores that occur inside the mouth. You can get them on 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.

Your mouth might tingle or burn before the actual 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 an inch across, although most of them are much smaller. Occasionally, someone who gets canker sores may also develop a fever and feel sluggish and uncomfortable.

The good news is that canker sores are not contagious like some other mouth sores, such as cold sores. So you can't spread canker sores by sharing food or kissing someone. Cold sores, however, are caused by the herpes simplex virus, which can pass from person to person. If you have a sore and you're wondering if it's of the cold or canker variety, just look at where it's located. Cold sores usually appear outside the mouth, around the lips, chin, or nostrils. Canker sores, on the other hand, are always found inside the mouth.

You can also have spots in your mouth when you have an infection such as chickenpox or measles. In some cases of these diseases the rash actually spreads into the mouth. But someone with chickenpox or measles would find spots on other parts of the body as well, easily distinguishing those rashes from canker sores.

What Causes Canker Sores?

No one is certain what causes canker sores. They often first appear between the ages of 10 and 20, although they can occur at any time in a person's life. 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 the sores show up 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 difference 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), a foaming agent found in most toothpastes and mouthwashes, can be associated with canker sores. Dietary deficiencies, such as not getting enough iron or vitamin B12, may also contribute to some cases of canker sores.

How Are They Treated?

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, there are some things you can do:

  • Various over-the-counter medicines can help to take the sting out of canker sores. Carbamide peroxide is a combination of peroxide and glycerin that cleans and coats the sore to protect it. Other over-the-counter remedies have benzocaine, menthol, and eucalyptol in them. These need to be applied repeatedly and may sting at first, but they can numb the sore and cut down on how long it lasts.
  • Try brushing and rinsing with toothpastes and mouthwashes that do not contain SLS.
  • Some homemade mouthwashes can ease pain as well. Try rinsing your mouth four times a day with a mixture of two ounces of hydrogen peroxide and two ounces of water or a combination of four ounces of water mixed with 1 teaspoon (5 milliliters) of salt and 1 teaspoon of baking soda. Swish the mixture in your mouth for about a minute and then spit it out — do not swallow it!
  • Dabbing a mixture of equal parts water and hydrogen peroxide directly on the sore, followed by a bit of milk of magnesia, may reduce discomfort and speed healing.
  • Some doctors suggest putting wet black tea bags on sores. Black tea contains tannin, a substance that can relieve pain. You can also find tannin in some over-the-counter medicines.

You'll want to watch what you eat when you have a canker sore. Spicy foods and acidic foods such as lemons or tomatoes can be extremely painful on these open wounds. So can anything sharp, such as nuts or potato chips, which can poke or rub the sore. Be careful when you brush your teeth, too. It's important to keep your mouth clean, but brushing the sore itself with a toothbrush will make it worse.

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, see your doctor or dentist. Your doctor 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.

Your doctor or dentist may prescribe a topical medicine or special mouthwash to help heal the sores. If the medicine needs to be 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. For severe mouth sores, your doctor or dentist may suggest other medications.

Although they can certainly be a pain, in most cases canker sores aren't that big of a deal.

Reviewed by: Lisa A. Goss, RDH, BS, and Charlie J. Inga, DDS
Date reviewed: December 2009

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Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor.

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