Symptoms:

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

Symptoms include:

• One or more painful, red spots or bump that develops into an open ulcer
• Middle of the sore is white or yellow
• Usually small (under 1 cm) but occasionally larger
• Sore may turn gray just before starting to heal

Less common symptoms include:

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

Pain usually goes away in 7 to 10 days. It can take 1 to 3 weeks for a canker sore to completely heal. Large ulcers can take longer to heal.

Sometimes, a severe outbreak of canker sores may be accompanied by nonspecific symptoms of illness, such as fever.

Signs and tests:

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 look for other causes, such as erythema multiforme, drug allergies, herpes infection, and bullous lichen planus.

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

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.