Millions of people suffer from recurrent painful mouth ulcers or canker sores, called aphthous stomatitis. Although many causes are known, there are few effective treatments.

A blister forms in the mouth and the top is quickly sloughed off, leaving a punched out whitish circular area that hurts to touch, particularly when food is in the mouth. Among the causes are infections including herpes, cytomegalovirus, yeast, and other viruses that have not even been identified.

They can also be caused by an autoimmune reaction in which a person's own immunity causes the blisters to form, and they have been reported to be caused by an allergy to chemicals in toothpastes or mouth washes. No studies have isolated bacteria or viruses often enough to blame them. However, some studies show a rise in a person's immunity against herpes and cytomegalovirus when the person suffers from these aphthous ulcers.

When you have an outbreak, your doctor may order blood tests that usually will be normal: antibody titre to herpes which are repeated two weeks later, and test for chronic infections such as hepatitis C and HIV. On rare occasions mouth ulcers can be a sign of Crohn's Disease (intestinal ulcers), certain cancers such as leukemia or lymphomas, or other immune defects.

The US Food and Drug Administration approved an oral paste called amlexanox (Aphthasol) to reduce swelling. The most effective treatment is for your doctor to inject a small amount of a type of cortisone called triamcinolone into each ulcer. It will get rid of the ulcers rather quickly, but it will not prevent them from recurring. Various journal articles have reported successful treatment with prednisone to supress immunity; pentoxifylline, a drug to increase blood flow to the mouth; thalidomide to reduce blood flow to the area; acyclovir to kill herpes; and colchicine, a gout medication. Check with your doctor.