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Canker Sores (Aphthous Ulcers)

Canker sores are small shallow ulcers that appear in the mouth and often make eating and talking uncomfortable. There are two types of canker sores:

  1. Simple canker sores. These may appear three or four times a year and last up to a week. They typically occur in people between 10 and 20 years of age.


  2. Complex canker sores. These are less common and occur more often in the people who have previously had them.

What causes canker sores?

The exact cause of most canker sores is unknown. Stress or tissue injury is thought to be the cause of simple canker sores. Certain foods—including citrus or acidic fruits and vegetables (such as lemons, oranges, pineapples, apples, figs, tomatoes, strawberries)—can trigger a canker sore or make the problem worse. Use of nonsteroidal anti-inflammatory drugs, like Motrin, is another common cause. Sometimes a sharp tooth surface or dental appliance, such as braces or ill-fitting dentures, might also trigger canker sores.

Some cases of complex canker sores are caused by an underlying health condition, such as an impaired immune system; nutritional problems, such as vitamin B-12, zinc, folic acid, or iron deficiency; and gastrointestinal tract disease, such as Celiac disease and Crohn's disease.

Are cold sores another name for canker sores?

No, although these sores are often confused for each other, they are not the same. Cold sores, also called a fever blister or herpes simplex type 1, are groups of painful, fluid-filled blisters. Unlike canker sores, cold sores are caused by a virus and are extremely contagious. Also, cold sores typically appear outside the mouth—usually, under the nose, around the lips, or under the chin while canker sores occur inside the mouth.

What are the symptoms of canker sores?

You may have a canker sore if you have:

  1. A painful sore or sores inside your mouth—on the tongue, soft palate (the back portion of the roof of your mouth), or inside your cheeks


  2. A tingling or burning sensation prior to the appearance of the sores


  3. Sores in your mouth that are round, white, or gray in color, with a red edge or border

In severe attacks, you may also experience:

  1. Fever


  2. Physical sluggishness


  3. Swollen lymph nodes

How are canker sores treated?

Pain from a canker sore generally lessens in a few days and the sores usually heal without treatment in about a week or two.

If sores are large, painful, or persistent, your dentist may prescribe an antimicrobial mouth rinse, a corticosteroid ointment, or a prescription or nonprescription solution to reduce the pain and irritation.

Can canker sores be prevented?

Although there is no cure for canker sores and they often reoccur, you may be able to reduce their frequency by:

  1. Avoiding foods that irritate your mouth—including acidic or spicy foods


  2. Avoiding irritation from gum chewing


  3. Brushing with a soft-bristled brush after meals and flossing daily, which will keep your mouth free of foods that might trigger a sore.

You should call your dentist if you have:

  1. Unusually large sores


  2. Sores that are spreading


  3. Sores that last 3 weeks or longer


  4. Intolerable pain despite avoiding trigger foods and taking over-the-counter pain medication


  5. Difficulty drinking enough fluids


  6. A high fever with the appearance of the canker sore(s)

Reviewed by the doctors at The Cleveland Clinic Department of Dentistry.

Reviewed by Jay H. Rosoff, DDS, on March 1, 2007

Edited by Charlotte E. Grayson, MD, on May 1, 2005.

Portions of this page © The Cleveland Clinic 2000-2005


Last Editorial Review: 11/20/2007