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Most canker sores are round or oval with a white or yellow center and a red border. They form inside your mouth — on or under your tongue, inside your cheeks or lips, at the base of your gums, or on your soft palate. You might notice a tingling or burning sensation a day or two before the sores actually appear.

There are several types of canker sores, including minor, major and herpetiform sores.

Minor canker sores

These most common canker sores:

  • Are usually small
  • Are oval shaped
  • Heal without scarring in one to two weeks

Major canker sores

These less common sores:

  • Are larger and deeper than minor canker sores
  • Have irregular edges
  • May take up to six weeks to heal and can leave extensive scarring

Herpetiform canker sores

These canker sores, which usually develop later in life:

  • Are pinpoint size
  • Often occur in clusters of 10 to 100 sores
  • Have irregular edges
  • Heal without scarring in one to two weeks

When to see a doctor

Consult your doctor if you experience:

  • Unusually large canker sores
  • Recurring sores, with new ones developing before old ones heal
  • Persistent sores, lasting three weeks or more
  • Sores that extend into the lips themselves (vermilion border)
  • Pain that you can't control with self-care measures
  • Extreme difficulty eating or drinking
  • High fever along with canker sores

See your dentist if you have sharp tooth surfaces or dental appliances that seem to trigger the sores.

Mar. 24, 2012