What causes Canker Sores?

A canker sore is a common form of mouth ulcer, which appears as a painful white or yellow ulcer surrounded by a bright red area. Canker sores usually heal without treatment within two weeks, and, unfortunately, we have no idea what causes them.

The medical term is apthous ulcers and they're round or oval painful ulcers that appear on the tongue, inner lips, inside of cheeks, or palate of the mouth. Up to 40 percent of people have experienced canker sores. So why have the remaining 60 percent never had them? We don't know.

Canker sores are more common in young people and occur more frequently in white people, non-smokers, women and people with high socioeconomic status. Why? We don't know. What we do know is that they aren't contagious and aren't caused by the herpes virus. (For a summery about the difference between canker sores and cold sores go to our Online Dental Education Library by clicking here.)

Some diseases cause canker sores to grow together and form larger ulcerations. People with AIDS, Bechets disease and even ulcerative colitis can experience large canker sores that can respond to immune suppressive drugs.

Other things that may contribute to canker sores are:

  • Injuries to the mouth, as seen frequently by contact sports players. Accidentally biting the inside of the cheek/lip may also result in a canker sore.
  • Spicy and/or acidic foods often produce a canker sore as a response to the irritation these spices and acids create in the mouth.
  • The use of chewing (smokeless) tobacco will often cause a canker sore to develop in the area of the mouth where the tobacco is held, due to the irritating chemicals found in the addictive product.
  • Poor-fitting, complete or partial dentures may cause canker sores in the area of the mouth where the denture may rubbing on the tissue. The development of a canker sore is often one of the first signs that indicate the need for a denture reline or adjustment by your dentist.
  • Orthodontic brackets, bands, and various other orthodontic attachments will often cause canker sores to develop in area of the mouth where there is constant friction on the oral tissues. This is common when orthodontic treatment first begins and may occur after each subsequent adjustments, throughout each stage of treatment.
  • Allergies to metals such as nickel may become evident in the mouth of a person wearing orthodontic devices necessary to move the teeth. Canker sores may begin to appear adjacent to the metal attachments. This is often referred to as contact dermatitis.
  • Emotional stress has been identified as a possible trigger that may cause the development of canker sores.
  • Bacteria responsible for peptic ulcers known as Helicobacter pylori, has been linked to canker sore occurrence.
  • Vitamin deficiencies, specifically vitamin B12, foliate (folic acid), and iron, may trigger canker sore development.
  • Hormonal changes, notably during menstruation, pregnancy, and menopause, have been linked to canker sores.
  • Canker sores often run in families. Genetics may be a factor for many canker sore sufferers.
  • Allergic reactions and sensitivities to certain foods may cause a canker sore to develop.

See a doctor immediately if your canker sores:

  1. Become unusually larger than normal.
  2. Are extremely painful, interfering with eating, drinking, and talking.
  3. Begin to appear more frequently than normal.
  4. Do not heal after 14 days.
  5. Are accompanied by a high fever.
  6. Appear to become infected.

For information on a variety of dental health topics go to our Online Dental Education Library .



A.D.A.M.: "Canker Sores"
Beyond Allergy: "Allergies to Metal in the Mouth" May 8, 2007.
Toni Brayer, MD: "Everything Health" Sept 6, 2010
About.com: "Dental Care"




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