Symptoms

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

Minor canker sores are the most common and:

• Are usually small
• Are oval shaped with a red edge
• Heal without scarring in one to two weeks

Major canker sores

Major canker sores are less common and:

• Are larger and deeper than minor canker sores
• Are usually round with defined borders, but may have irregular edges when very large
• Can be extremely painful
• May take up to six weeks to heal and can leave extensive scarring

Herpetiform canker sores

Herpetiform canker sores are uncommon and usually develop later in life, but they're not caused by herpes virus infection. These canker sores:

• Are pinpoint size
• Often occur in clusters of 10 to 100 sores, but may merge into one large ulcer
• 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, or frequent outbreaks
• Persistent sores, lasting two 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.