A canker sore is a painful, open sore in the mouth. Canker sores are white or yellow and surrounded by a bright red area. They are benign (not cancer).

See also: Herpes, Fever blisters and Canker sores

Canker sores are a common form of mouth ulcer. They occur in women more often than men. They may occur at any age, but usually first appear between the ages of 10 and 40.

Canker sores usually appear on the inner surface of the cheeks and lips, tongue, soft palate, and the base of the gums.

Canker sores can run in families. They may also be linked to problems with the body's immune (defense) system. The sores may occur after a mouth injury due to dental work, aggressive tooth cleaning, or biting the tongue or cheek.

Canker sores can be triggered by emotional stress, dietary deficiencies (especially iron, folic acid, or vitamin B-12), menstrual periods, hormonal changes, food allergies, and similar situations. They occur most commonly with viral infections. In some cases, the cause can not be identified.

The first symptom is usually a tingling or burning sensation that you feel before other symptoms develop.

The following symptoms may then occur:

• Painful, red spot or bump that develops into an open ulcer
  • Center is colored white or yellow
  • Usually small (under 1 cm) but occasionally larger
  • Single bump or group of bumps (crops)
• Sore may turn gray just before starting to heal

• Fever
• General discomfort or uneasiness (malaise)
• Swollen lymph nodes

Pain decreases in 7 to 10 days, with complete healing in 1 to 3 weeks. Particularly large ulcers (greater than 1 cm in diameter) often take longer to heal (2 to 4 weeks). Occasionally, a severe occurrence may be accompanied by nonspecific symptoms of illness, such as fever. Canker sores often return.

Your health care provider can often make the diagnosis by looking at the sore. If canker sores persist or continue to return, tests should be done to rule out other causes, such as erythema multiforme, drug allergies, herpes infection, bullous lichen planus, and other disorders.

Canker sores are not cancer and do not cause cancer. There are types of cancer, however, that may first appear as a mouth ulcer that does not heal. See: Squamous cell carcinoma.

A biopsy may be used to distinguish a canker sore from other causes of mouth ulcers.

Treatment is usually not necessary. In most cases, the canker sores go away by themselves.

If you have a canker sore, you should not eat hot or spicy foods, which can cause pain. Mild, over-the-counter mouth washes or salt water may help. There are over-the-counter medicines that soothe the painful area. These medicines are applied directly to the sore area of the mouth.

The easiest home remedy is a mixture of half hydrogen peroxide and half water. Use a cotton swab to apply the mixture directly to the canker sore. Then, dab a small amount of Milk of Magnesia on the canker sore, three to four times a day. This is soothing and may also help it heal.

Another home remedy is to mix half Milk of Magnesia and half Benadryl liquid allergy medicine. Swish this mixture in your mouth for about 1 minutes, then spit it out.

Other treatments for more severe cases include applying fluocinonide gel (Lidex) or chlorhexidine gluconate mouthwash. Powerful anti-inflammatory medicines called corticosteroids are sometimes used.

To prevent bacterial infection, brush and floss your teeth regularly and visit the dentist for routine care.

Canker sores usually heal on their own. The pain usually decreases in a few days. Other symptoms disappear in 10 to 14 days.

Antibiotic treatment for canker sores may lead to oral thrush (a type of mouth infection) or other Candida infections. Rarely, bacterial infections such as cellulitis and Ludwig's angina may occur.

Canker sores are not cancer and don't lead to cancer. But if you have a mouth ulcer lasts more that 2 weeks, you should see your doctor to rule out possible cancer.

Apply home treatment and call your health care provider if symptoms of canker sores persist or worsen, or canker sores recur more often than 2 or 3 times per year.

Call your health care provider if symptoms are associated with other problems such as fever, diarrhea, headache, or skin rash.

Femiano F, Lanza A, Buonaiuto C, et al. Guidelines for diagnosis and management of aphthous stomatitis. Pediatr Infect Dis J. 2007;26:728-732.

Gonsalves WC, Chi AC, Neville BW. Common oral lesions: Part I. Superficial mucosal lesions. Am Fam Physician. 2007;75(4):501-507.