What are canker sores?

Quick Answer
Small, round ulcers of the mucous membranes that line the mouth.
Expert Answers
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Causes and Symptoms

Aphthous ulcers are the most common lesions of the mucous membranes that line the mouth. The exact cause of this easily recognized problem is unknown; however, some evidence points to infection with the human herpesvirus 6, one of a family of viruses that cause a variety of diseases, including cold sores, genital herpes, and shingles. Possible triggers may include mouth injury, stress, vitamin deficiency, hormonal changes, and food allergies.

In most cases, a canker sore is a painful, small, round ulcer on a red base with a yellowish center. The redness also surrounds the lesion like a halo. Sores are usually about one to two millimeters in diameter but may be as large as one to two centimeters. They may occur as either single or multiple lesions and are found on the mucous membranes lining the mouth and tongue. These lesions tend to recur; the recurrences may be associated with stress or illness. The associated pain usually lasts for a week to ten days, and the ulcers heal completely within three weeks. Major aphthous ulcers, another variety, start out as nodules under the mucous membranes, which then break down and form craterlike ulcers that may last more than a month.

Aphthous ulcers may occur on their own, but they may also be associated with some diseases and disorders of the collagen, gastrointestinal problems such as Crohn's disease, bacterial infections, and Behçet’s disease. This last condition is a syndrome that involves painful ulcers of the tongue and oral mucous membranes, in addition to a variety of eye, skin, joint, gastrointestinal, and central nervous system problems.

Treatment and Therapy

The treatment of canker sores is geared toward relieving the associated pain rather than curing the lesion. Treatments include a steroid-containing gel or paste applied directly to the ulcer, an anesthetic spray, or a mouthwash that the patient “swishes and spits.” Oral antibiotic rinses may be prescribed; however, an oral infection known as "candidiasis" or "thrush" may develop as a result. In severe cases, oral steroids tapered over one week may provide relief.

Perspective and Prospects

In patients with human immunodeficiency virus (HIV) infection, aphthous ulcers may be extremely painful or extensive. If the ulcers do not respond to conventional treatment, then the drug thalidomide may be useful. However, it must be used with extreme caution, as this drug is known to cause severe birth defects if taken during pregnancy.


A.D.A.M. Medical Encylopedia. "Canker Sore." MedlinePlus, February 17, 2011.

AAOM Web Writing Group. "Canker Sores." American Academy of Oral Medicine, December 31, 2007.

Komaroff, Anthony, ed. Harvard Medical School Family Health Guide. New York: Free Press, 2005.

National Institute of Dental Research. Fever Blisters and Canker Sores. Rev. ed. Bethesda, Md.: National Institutes of Health, 1992.

National Institute of Dental and Craniofacial Research. "Mouth Problems and HIV." National Institutes of Health, March 25, 2011.

Norwood, Diane, and Michael Woods. "Aphthous Ulcers." Health Library, November 26, 2012.

Porter, Robert S., et al., eds. The Merck Manual Home Health Handbook. Whitehouse Station, N.J.: Merck Research Laboratories, 2009.

Sutton, Amy L., ed. Dental Care and Oral Health Sourcebook. 3d ed. Detroit, Mich.: Omnigraphics, 2008.