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, under your tongue, or on your gums, lips, tongue, or roof of your mouth.

What is the cause?

The exact cause of canker sores is not known. Some possible causes are:

• Not getting enough of certain nutrients in your diet, such as vitamin B12, folic acid, and iron
• Biting your tongue or cheek
• Hot foods or drinks
• An immune system problem
• An allergic reaction to food, medicine, or bacteria
• Feeling stressed

Canker sores are not the same as cold sores. Cold sores are caused by a virus and are very contagious. Cold sores are usually on or next to the lips, and look more like blisters.

What are the symptoms?

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

How is it diagnosed?

Your healthcare provider will ask about your symptoms and medical history and examine you. Your provider may use a swab to take a sample of cells from the sore to check for bacteria or a virus.

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 nonprescription pain medicine, such as acetaminophen. Acetaminophen may cause liver damage or other problems. Read the label carefully and take as directed. Unless recommended by your provider, don’t take more than 3000 milligrams (mg) in 24 hours or take it for longer than 10 days. To make sure you don’t take too much, check other medicines you take to see if they also contain acetaminophen. Ask your provider if you need to avoid drinking alcohol while taking this medicine.
• Rinse your mouth with an anesthetic mouthwash–for example, a mouthwash containing lidocaine.
• Drink plenty of fluids.
• Take vitamins as recommended by your healthcare provider.

If the sores cause so much pain that it is hard to eat or drink, a nonprescription medicine (for example, a medicine with benzocaine) may be put on the sores to stop the pain and help them heal faster. Your provider may prescribe other medicine to help the sores go away more quickly.

Canker sores usually heal without special treatment in a week or two. The sores do not cause scarring.

How can I take care of myself?

• Avoid spicy or salty foods, hard or sharp foods (such as toast or potato chips), hot drinks, 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.
• Mix 1 tablespoon of baking soda with enough water to make a thin paste you can put on the sore.
• Use only soft-bristle toothbrushes when you brush your teeth. Gently brush your teeth and gums often.
• Learn ways to manage stress.
• Avoid biting the inside of your cheeks.