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Recurrent canker sores afflict about 20 percent of the general population. The medical term for the sores is aphthous stomatitis. Canker sores are usually found on the movable parts of the mouth such as the tongue or the inside linings of the lips and cheeks. They begin as small oval or round reddish swellings, which usually burst within a day. The ruptured sores are covered by a thin white or yellow membrane and edged by a red halo. Generally, they heal within 2 weeks. Canker sores ranged in size from an eighth of an inch wide in mild cases to more than an inch wide in severe cases. Severe canker sores may leave scars. Fever is rare, and the sores are rarely associated with other diseases. Usually a person will have only one or a few canker sores at a time.

Most people have their first bout with canker sores between the ages of 10 and 20. Children as young as 2, however, may develop the condition. The frequency of canker sore recurrences varies considerably. Some people have only one or two episodes a year, while others may have a continuous series of canker sores.

What causes canker sores?

The cause of canker sores is not well understood. More than one cause is likely, even for individual patients. Canker sores do not appear to be caused by viruses or bacteria, although an allergy to a type of bacterium commonly found in the mouth may trigger them in some people. The sores may be an allergic reaction to certain foods. In addition, there is research suggesting that canker sores may be caused by a faulty immune system that uses the body’s defenses against disease to attack and destroy the normal cells of the mouth or tongue.

British studies show that in about 20 percent of patients, canker sores are partly nutritional deficiencies, especially lack of vitamin B12, folic acid and iron. Similar studies performed in the United States, however, have not confirmed such findings. In a small percentage of patients, canker sores occur with gastrointestinal problems, such as an inability to digest certain cereals. In these patients, canker sores appear to be part of a generalized disorder of the digestive tract.

Female sex hormones apparently play a role in causing canker sores. Many women have bouts of the sores during certain phases of their menstrual cycles. Most women experience improvement or remission of their canker sores during pregnancy. Researches have used the hormone therapy successfully in clinical studies to treat some women. Both emotional stress and injury to the mouth can trigger outbreaks canker sores, but these factors probably do not cause the disorder.

Who is susceptible?

Women are more likely than men to have recurrent canker sores. Genetic studies show that susceptibility to recurrent outbreaks of the sores is inherited in some patients. This partially explains why the disorder is often shared by family members.

What are the treatments for canker sores?

Some doctors recommend that patients who have frequent bouts of canker sores undergo blood and allergy tests to determine if their sores are caused by a nutritional deficiency, and allergy or some preventable cause. Vitamins and other nutritional supplements often prevent recurrences or reduce the severity of canker sores in patients with a nutritional deficiency. Patients with food allergies can reduce the frequency of canker sores by avoiding these foods. There are several treatments for reducing the pain and duration of canker sores for patients whose outbreaks cannot be prevented. These include numbing ointments such as benzocaine, which are available in drug stores without a prescription. Anti-inflammatory steroid mouth rinses or gels can be prescribed for patients with severe sores.

Mouth rinses containing antibiotic tetracycline may reduce the unpleasant symptoms of canker sores and speed healing by preventing bacterial infections in the sores. Patients with severe recurrent canker sores may need to take steroid or other immunosuppressant drugs orally. These potent drugs can cause man undesirable side effects, and should be used only under the close supervision of a dentist or physician.

What can patients do?

If you have canker sores, avoid abrasive foods such as potato chips that can stick in the cheek or gum and aggravate the sores. Take care when brushing your teeth not to stab the gum with a toothbrush bristle. Avoid acidic and spicy foods. Canker sores are not contagious, so patients do not have to worry about spreading them to other people.