Aphthous ulcer

Alternative names
Ulcer - aphthous; Canker sores

A canker sore is an open sore in the mouth, which appears as a painful white or yellow ulcer surrounded by a bright red area. A canker sore is benign (not harmful). See also herpes, which can also cause mouth sores.

Causes, incidence, and risk factors

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.

They usually begin with a tingling or burning sensation, followed by a red spot or bump that ulcerates. 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 or malaise. Canker sores often come back again in the future.

There may be an inherited tendency to develop canker sores, as they often run in families. There may also be an immune system link. Ulcers may develop in response to a mouth injury such as dental procedures or aggressive tooth cleaning.

Canker sores may also occur at the site of a bite when the tongue or cheek is bitten. They can be triggered by emotional stress, dietary deficiencies (especially iron, folic acid, or vitamin B12), menstrual periods, hormonal changes, food allergies, and similar situations. They occur most commonly with viral infections. They may occur with no identifiable cause.


  • A burning or tingling sensation before other symptoms develop (warning symptom)  
  • Skin lesion on mucous membranes of the mouth       o Begins as a red spot or bump       o Then develops into an open ulcer           + Usually small, 1-2 mm to 1 cm           + Occasionally larger than 1 cm           + Single or clusters, often appears in groups (crops)       o Painful       o Center appears white or yellow with fibrous texture       o Halo border is bright red (a red halo may not always be present)       o May have gray membrane just prior to healing

Less common symptoms, which may appear at the time of the canker but may or may not be related, include:

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

Signs and tests

A diagnosis is based on the distinctive appearance of the lesion. If canker sores persist or continue to return, a health care provider or dentist should be consulted to rule out other causes of mouth ulcers. (These include erythema multiforme, drug allergies, herpes simplex infection, pemphigus, pemphigoid, bullous lichen planus, and other disorders.)

Squamous cell carcinoma may first appear as a mouth ulcer that does not heal, but this is rare. A relatively new ulcer-like condition is hairy leukoplakia, a condition that occurs with HIV infection and may be mistaken for the common canker.

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


Treatment is usually not necessary. In most cases, the condition is self-limited and healing is spontaneous.

Severe mouth ulcers (larger than 1 cm or lasting longer than 2 weeks) may require evaluation and treatment. In these cases, topical or oral (by mouth) tetracycline suspension may be given, with instructions to hold it in the mouth for 2 to 5 minutes before swallowing.

Tetracycline is usually not prescribed for children until after all the permanent teeth have fully developed. If children use tetracycline suspension before their permanent teeth are fully developed, it can permanently discolor teeth that are still forming. Multiple, painful mouth ulcers may treated with an antiviral agent such as acyclovir.

Topical or oral corticosteroids are rarely used, but they may reduce inflammation. Dexamethasone suspension may be given with instructions to rinse the mouth and spit it out; or dexamethasone, prednisone, or other corticosteroid may be given systemically.

Avoid hot or spicy foods to minimize discomfort. Mild mouth washes such as salt water or over-the-counter mouth washes may help. Over-the-counter topical medications (applied to a specific area of the mouth) may reduce discomfort and soothe the ulcerated area.

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

The easiest home remedy is to apply hydrogen peroxide (1 part hydrogen peroxide and one part water with a cotton swab) on the canker sore. Then dab a small amount of milk of magnesia on the canker 3-4 times a day. This is not only soothing, but appears to help healing.

Expectations (prognosis)
Canker sores usually heal spontaneously. The pain usually decreases in 3 or 4 days. Other symptoms disappear in 10 to 14 days.


  • Oral thrush or other Candida infections may occur following the use of antibiotic treatment for cankers  
  • Rarely, secondary bacterial infections may occur (cellulitis, Ludwig’s angina)  
  • Oral cancer is not a complication of canker sores, but if an ulcer lasts more that 2 weeks, cancer may actually be the cause of the ulcer. Therefore, any ulcer lasting over 2 weeks should be evaluated by a physician.

Calling your health care provider
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.

Johns Hopkins patient information

Last revised: December 5, 2012
by Potos A. Aagen, M.D.

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