how do canker sores occur
The sores may occur singly or in groups and vary from about 1/8 inch to 1 -1/4 inch in diameter. The sore may be painful for three or four days, but complete healing usually takes ten to fifteen days. Canker sores may recur many times each year. Causes: No one knows what causes canker sores. They may be caused by a virus, may be a form of allergic reaction or may result from an auto-immune condition (meaning that the body has developed an immune reaction against its own tissue).