Canker sores, also called aphthous ulcers, are small, shallow lesions that develop on the soft tissues in your mouth or at the base of your gums. Unlike cold sores, canker sores don’t occur on the surface of your lips and they aren’t contagious. They can be painful, however, and can make eating and talking difficult.

Most canker sores go away on their own in a week or two. Check with your doctor or dentist if you have unusually large or painful canker sores or canker sores that don’t seem to heal.

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:

Major canker sores

Major canker sores are less common and:

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:

When to see a doctor

Consult your doctor if you experience:

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

The precise cause of canker sores remains unclear, though researchers suspect that a combination of factors contributes to outbreaks, even in the same person.

Possible triggers for canker sores include:

Canker sores may also occur because of certain conditions and diseases, such as:

Unlike cold sores, canker sores are not associated with herpes virus infections.

Anyone can develop canker sores. But they occur more often in teens and young adults, and they’re more common in females.

Often people with recurrent canker sores have a family history of the disorder. This may be due to heredity or to a shared factor in the environment, such as certain foods or allergens.

Canker sores often recur, but you may be able to reduce their frequency by following these tips:

Tests aren’t needed to diagnose canker sores. Your doctor or dentist can identify them with a visual exam. In some cases, you may have tests to check for other health problems, especially if your canker sores are severe and ongoing.

Treatment usually isn’t necessary for minor canker sores, which tend to clear on their own in a week or two. But large, persistent or unusually painful sores often need medical care. A number of treatment options exist.

Mouth rinses

If you have several canker sores, your doctor may prescribe a mouth rinse containing the steroid dexamethasone (dek-suh-METH-uh-sown) to reduce pain and inflammation or lidocaine to reduce pain.

Topical products

Over-the-counter and prescription products (pastes, creams, gels or liquids) may help relieve pain and speed healing if applied to individual sores as soon as they appear. Some products have active ingredients, such as:

There are many other topical products for canker sores, including those without active ingredients. Ask your doctor or dentist for advice on which may work best for you.

Oral medications

Oral medications may be used when canker sores are severe or do not respond to topical treatments. These may include:

Cautery of sores

During cautery, an instrument or chemical substance is used to burn, sear or destroy tissue.

Nutritional supplements

Your doctor may prescribe a nutritional supplement if you consume low amounts of important nutrients, such as folate (folic acid), vitamin B-6, vitamin B-12 or zinc.

Related health problems

If your canker sores relate to a more serious health problem, your doctor will treat the underlying condition.

To help relieve pain and speed healing, consider these tips:

Your doctor or dentist can diagnose a canker sore based on its appearance. Here’s some information to help you get ready for your appointment.

Information to gather

Before your appointment make a list of:

Here are some basic questions to ask:

Don’t hesitate to ask any other questions during your appointment.

What to expect from your doctor or dentist

Be ready to answer questions from your doctor or dentist, such as:

© 1998-2024 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved.

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