Anything that affects the lining of the mouth can precipitate canker sores. It may be physical damage such as a scratch by a nut or a stray toothbrush bristle, a bruise or a burn from hot food. Food allergies may also be a factor. Some people avoid chocolate, walnuts or acidic foods such as citrus fruit, tomatoes and vinegar because they seem to trigger the ulcers. Canker sores are not known to be contagious.
Women are twice as likely to have canker sores as men.
There is nothing that will stop canker sores from recurring. However, there are things that can be done to relieve the discomfort and to prevent an infection in the area, during the 3-4 days when the sores are likely to be painful. Two cleansing antiseptic mixtures are hydrogen peroxide diluted with water to half-strength and one teaspoon each of salt and baking soda to four ounces of water. These should be used as rinses or gargles four times a day. It is also helpful to avoid acidic foods that may irritate the sores.