Unknown: Canker Sores

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Unknown: Canker Sores


Canker sores are small ulcers inside the mouth that are white or grayish with red borders. They are not contagious. Canker sores should not be confused with cold sores, which occur outside the mouth around the lips, are caused by a virus, and are very contagious.


Canker sores are small patches of raw skin on the tissues that line the cheeks and the inside of the lips. They may also occur at the base of the gums or below the tongue on the floor of the mouth. They may appear as single ulcers or in clusters. Most are about three-eighths of an inch (1 centimeter) wide, but some are larger.

Doctors classify canker sores into three groups: minor sores, which are smaller than half an inch (1.3 centimeters) and heal by themselves in seven to ten days; major sores, which are larger than half an inch (1.3 centimeters), are usually deeper than minor sores, may take as long as a month to heal, and may leave scars; and herpetiform sores, which are small, form clusters that look like the fever blisters caused by herpes viruses, and heal in about a week. About 80–85 percent of canker sores are minor sores, 10 percent are major sores, and 5–10 percent are herpetiform.


Canker sores are most common in children over ten years of age and young adults. They are estimated to occur in 30–60 percent of the general population. They appear to be equally common in all races and ethnic groups but are slightly more common in women of childbearing age than in men. Herpetiform sores are more common in older people than in younger patients.

Canker sores appear to run in families even though they are not contagious; about 50 percent of people who have frequent occurrences of canker sores have relatives with the same problem. People with certain digestive disorders, including Crohn disease, irritable bowel syndrome, and celiac disease, are also at increased risk of recurrent canker sores.

Causes and Symptoms

The exact cause of canker sores is not known; however, some doctors think that the sores develop when the person's immune system targets the tissues of the mouth. There are a number of possible factors that may trigger such a reaction:

  • Trauma. Canker sores sometimes develop when a person's mouth is irritated by poorly fitted dentures, loose wires from orthodontic braces, a rough tooth, or accidentally biting the inside of the mouth. Brushing too hard or using a very stiff toothbrush have also been associated with damage to the lining of the mouth and canker sores.
  • Nutritional deficiencies. People who are not getting enough vitamin B12, iron, zinc, or folic acid in their diet are more likely to develop canker sores.
  • Infection by Helicobacter pylori, the same bacterium that causes stomach ulcers.
  • Stress. Researchers have noted that high-achieving people and people with higher-than-average anxiety levels are more likely to develop canker sores.
  • In women, hormonal changes during menstruation and pregnancy are often associated with an outbreak of canker sores.
  • AIDS and other disorders that affect the immune system.
  • Food allergies. Flavoring agents, essential oils, benzoic acid, cinnamon, gluten, cow's milk, coffee, chocolate, potatoes, cheese, figs, nuts, citrus fruits, and certain spices have all been associated with canker sores in some people.
  • Sensitivity to certain chemicals found in toothpastes and mouthwashes, particularly sodium lauryl sulfate (SLS), a chemical added to toothpaste to thicken it and create a lather during brushing.

Canker sores are preceded by one or two days of tingling or a mild pain in the area where the sore is developing. The reddened area then turns into a whitish patch of broken skin surrounded by a reddish rim. The area in the middle of the sore that looks white or grey is actually partially destroyed. This is the reason why anything containing acids (fruit juices, sodas, coffee), is hot, or is heavily spiced can cause considerable pain if it touches the sore. Some people find it difficult to brush their teeth, talk, or eat until the sore heals.


The doctor or dentist will usually diagnose canker sores on the basis of their appearance inside the mouth. If the sores do not heal or become more severe, a sample of tissue may be taken to check for other possible mouth disorders. Patients with AIDS, for example, may have an infection in the mouth along with the canker sores. In a very few cases, a sore that does not heal is a symptom of cancer.

When to Call the Dentist

Canker sores, particularly minor sores, usually heal without difficulty even though they may be painful for a week or so. Patients should, however, see their dentist or doctor if they have any of the following symptoms, which are not normal for ordinary canker sores:

  • Fever, particularly fever of 101°F (38.3°C) or higher
  • Headache
  • Pains in the muscles and joints
  • Unusually large sores
  • New sores developing before old ones heal
  • Sores that extend outward from the lining of the mouth into the lips
  • Pain that cannot be controlled by ordinary self-care treatments
  • Severe difficulty in eating or drinking
  • Nausea, vomiting, or diarrhea
  • Sore throat or swollen glands in the neck
  • Rash on the face or body


Minor canker sores will heal eventually without treatment, although dentists frequently prescribe a mouthwash that contains a steroid medication or a rinse that contains an antibiotic. The antibiotic rinse is not

usually given to children because it can cause their teeth to discolor. Other treatments include pastes like Orabase, Aphthasol, or Lidex. These can be applied directly to the sore to speed healing and protect the sore from further irritation by food, tooth brushing, or orthodontic braces. The dentist may also prescribe mouthwashes or gels that contain a local anesthetic. The gels can be applied directly to the sore with a cotton swab.

Patients can also care for canker sores at home by making a solution of 1 teaspoon of salt in a pint of warm water and using it to rinse out the mouth as often as desired. Other home remedies that work for some people include making a paste of baking soda and water to be applied to the sores; allowing small chips of ice to melt slowly over the sores; or applying a small amount of milk of magnesia to the sores several times a day.

Patients with severe canker sores may be treated with steroid medications injected directly into the tissues under the sores. Some dentists have used lasers to treat severe canker sores in patients who do not respond to other forms of treatment. Laser therapy gives good results in treating canker sores but is considered experimental because it requires specialized training to use effectively.

Other treatments that are beneficial for some patients include vitamin and mineral supplements, zinc lozenges, stress management techniques, and avoiding foods that are likely to irritate the mouth. For many people, these “problem foods” include nuts, chips, pretzels, certain spices, salty foods, tomatoes, and citrus fruits.


Most canker sores heal on their own in one to two weeks, although major sores may take as long as a month to heal completely. Patients with sores that do not respond to any treatment, take longer than a month to heal, or do not heal at all should see their doctor or dentist as soon as possible.


There is no way to completely prevent canker sores in people who are susceptible to them because of family history or an underlying disease condition like AIDS. However, maintaining good oral hygiene, eating a nutritious diet, using softer toothbrushes, and checking with the dentist

to be sure that braces or dentures are fitted properly can all help to lower the risk of canker sores.

The Future

Canker sores are a common health problem that is likely to affect about a third of the general population for the foreseeable future. Further advances in laser therapy may offer a new treatment option for people with recurrent or severe canker sores.

SEE ALSO AIDS; Allergies; Celiac disease; Cold sore; Crohn disease; Irritable bowel syndrome


Aphthous ulcer: The medical term for canker sore.

Herpetiform: Resembling blisters caused by herpes.

Stomatitis: The medical term for an inflammation of the mouth.

For more information


Smith, Rebecca W. Columbia University School of Dental and Oral Surgery's Guide to Family Dental Care. New York: W.W. Norton, Inc., 1997.


Brody, Jane E. “Personal Health: Canker Sores.” New York Times, June 10,1987. Available online at http://query.nytimes.com/gst/fullpage.html?res=9B0DE5DA1138F933A25755C0A961948260&sec=&spon=&pagewanted=all (accessed May 13, 2008).


American Academy of Family Physicians (AAFP) Patient Information. Canker Sores—What Are They and What Can You Do about Them?. Available online at http://www.aafp.org/afp/20000701/160ph.html (posted July 1, 2000; accessed May 13, 2008).

American Dental Association (ADA). Common Mouth Sores. Available online at http://www.ada.org/public/topics/mouth_sores.asp#faq (accessed May 13, 2008).

Mayo Clinic. Canker Sore. Available online at http://www.mayoclinic.com/health/canker-sore/DS00354 (updated January 31, 2008; accessed May 13, 2008).