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Canker Sore

What is a canker sore?

Canker sores are painful sores in your mouth. They can be very tiny or up to a half inch wide. They may form on the inside of your cheeks or on your gums, lips, tongue, floor of your mouth, or roof of your mouth.

How does it occur?

The exact cause of canker sores is not known. Sometimes they may occur because you are not getting enough of certain nutrients in your diet, such as vitamin B12, folic acid, and iron. Other possible causes are biting your tongue or cheek, hot foods or drinks, a reaction to viruses or bacteria, an immune system problem, or food allergies. You may find that you are more likely to have canker sores when you are feeling stressed.


Canker sores are different from cold sores. Cold sores are caused by a virus. They usually occur at the border between the lip and the skin above it and they are more common on the upper lip. Canker sores are not contagious but cold sores are.

What are the symptoms?

They usually appear without warning as a painful sore. Canker sores can take many shapes but they are usually round or oval with a yellowish center. They may have a raised red border. They are painful and very sensitive to touch and to spicy or salty foods.

How is it diagnosed?

Your healthcare provider will ask about your symptoms and examine you. If your provider is not sure of the diagnosis, a sample of cells from the sore may be sent to the lab to check for bacteria or viruses as a possible cause.

How is it treated?

Because the cause of canker sores is not known, there is no specific treatment to cure them. It may help to take a nonprescription pain-relief medicine, such as acetaminophen. You can also to rinse your mouth with an anesthetic mouthwash (for example, a mouthwash containing lidocaine). If the sores cause so much pain that it is hard to eat or drink, your provider may prescribe stronger pain-relief medicine.


Your provider may prescribe a steroid cream or tablet to help the sores go away more quickly.

How long will the effects last?

Canker sores usually heal without special treatment in a week or two. You may recover sooner if you drink plenty of fluids, take vitamins, and avoid stress. The sores do not cause scarring.

How can I take care of myself?

  • Avoid spicy or salty foods, coffee, and citrus fruits.
  • Put ice on the sore to relieve the pain.
  • Rinse your mouth with the mouthwash recommended by your healthcare provider. You may also rinse with a mixture of 1 tablespoon of hydrogen peroxide in 8 ounces (240 milliliters) of water, or put a thin paste of baking soda and water on the sore. Do this between meals and before bed (4 times a day).
  • For infants, give fluids by cup or spoon rather than from a bottle because sucking can be painful.

How can I help prevent canker sores?

Because the exact cause of canker sores is not known, there is no sure way to prevent them. However, the following measures may help:

  • Use only soft-bristle toothbrushes when you brush your teeth and gently brush your teeth and gums often.
  • Try to avoid stress.
  • Take a daily multivitamin.
  • Avoid biting the inside of your cheeks.

Disclaimer: This content is reviewed periodically and is subject to change as new health information becomes available. The information provided is intended to be informative and educational and is not a replacement for professional medical evaluation, advice, diagnosis or treatment by a healthcare professional.


HIA File oral4853.htm Release 13/2010

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