Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

What are canker sores?

Canker sores are small shallow ulcers that occur in the lining of the mouth. The medical term for canker sores is “aphthous ulcers.” Canker sores start as white to yellowish ulcers that are surrounded by redness. They are usually very small (less than 1 mm) but may enlarge to ½ to 1 inch in diameter. Canker sores can be painful and often make eating and talking uncomfortable. There are 2 types of canker sores:

  • Simple canker sores: These may appear 3 or 4 times a year and last up to a week. Anyone can get canker sores. However, canker sores typically occur in people between 10 and 20 years of age.
  • Complex canker sores: These are less common and occur more often in the people who have previously had them.

What causes canker sores?

The exact cause of most canker sores is unknown. A stress or minor injury to the inside of the mouth is thought to be the cause of simple canker sores. Certain foods —including citrus or acidic fruits and vegetables (such as lemons, oranges, pineapples, apples, figs, tomatoes, strawberries) — can trigger a canker sore or make the problem worse. Use of nonsteroidal anti-inflammatory drugs, like ibuprofen (Advil®, Motrin®), is another common cause. Sometimes a sharp tooth surface or dental appliance, such as braces or ill-fitting dentures, might also trigger the sores.

Some cases of complex canker sores are seen in patients with diseases of the immune system. These diseases include lupus, Behcet's disease, inflammatory bowel diseases (including celiac disease, ulcerative colitis, and Crohn’s disease), and AIDS. Canker sores are also seen in patients with nutritional problems, such as a deficiency in vitamin B-12, zinc, folic acid, or iron.

What are the symptoms of canker sores?

You may have a canker sore if you have:

  • A painful sore or sores inside your mouth — on the tongue, soft palate (the back portion of the roof of your mouth), or inside your cheeks.
  • A tingling or burning sensation prior to the appearance of the sores.
  • Sores in your mouth that are round, white, or gray in color, with a red edge or border.

In severe attacks, you may also experience:

  • Fever.
  • Physical sluggishness.
  • Swollen lymph nodes.