These sores generally heal within 2 weeks. Severe forms of the sores may leave scars. Most people experience their first bout with canker sores when they are between the ages of 10 and 20 although children as young as 2 years of age may develop the condition. The frequency of canker sore recurrences varies considerably. Some people may only experience one or two episodes a year, whereas others may have a continuous series of canker sores.
Most people experience tingling or pain in the area of the mouth where canker sores later develop.
It is not known what causes canker sores in all patients although more than one cause is likely even for individual patients. Attempts to find bacteria or viruses linked with the disease have not proven fruitful although an allergy to a type of bacteria commonly found in the mouth may cause some people to develop canker sores. The sores might also be an allergic reaction to certain foods eaten. In addition, there is research that suggests 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 indicate that canker sores in about 20 percent of all patients are partially caused by nutritional deficiencies, especially a lack of vitamin B12, folic acid and iron.