Canker Sores

What Is It?

This disease causes painful, round ulcers to develop on the linings of the cheeks and lips, the tongue or the base of the gums. The tendency to develop these ulcers is inherited. Ulcers also can be associated with other diseases, particularly connective tissue diseases such as lupus or Behçet's syndrome, which cause symptoms on the eyes and genitals as well as the mouth. There can be one or many ulcers at the same time, and they are recurrent, which means they keep returning. Multiple ulcers are scattered across the lining of the mouth, not clustered. Most people get one to three of these lesions at each episode, but a small number of people get more than a dozen ulcers at a time.

The cause of canker sores is not known, but most theories involve an immune abnormality. Certain blood diseases, vitamin and mineral deficiencies, allergies, trauma and Crohn's disease cause similar ulcers. Canker sores are often confused with cold sores, which are caused by a herpes virus.

Approximately 17% of the population has recurrent aphthous stomatitis, which is classified into three categories:

  • Minor ulcers are less than 1 centimeter (slightly less then ½inch) in diameter and do not leave scars. The sores usually heal within two weeks.
  • Major ulcers (also called Sutton's disease) are almost ½ inch or more in diameter, take longer than minor ulcers to heal and may leave scars.
  • Herpetiform ulcers are clusters of dozens of smaller ulcers. This form is rare.

People tend to have two to six ulcers per episode and have several episodes each year. For most people, canker sores are merely an annoyance, but some people experience large, painful, frequent sores that can reach 2 to 4 centimeters in diameter. The ulcers can interfere with speech and eating and can last for weeks to months, causing significant pain and disability. When they do heal, they may leave scars that can make it more difficult to move the tongue and can destroy oral tissue.


You may feel a burning or tingling sensation in an area of inflammation before an ulcer appears. An ulcer takes two to three days to form completely. The sores are round, shallow and symmetric, which means they are the same on all sides. The are painful. They usually are found on the inner part of the lips and cheeks and the tongue.


Canker sores are the most common recurring oral ulcers and are diagnosed mostly by process of elimination. If the ulcers become more frequent or severe, are accompanied by other symptoms (such as rashes, joint pain, fevers or diarrhea) or are larger than about ½inch in diameter, you should visit your dentist or physician. He or she will try to rule out blood diseases, connective tissue diseases, drug reactions and skin disorders. A biopsy and blood tests may be required to rule out other conditions or diseases.

Expected Duration

The painful stage lasts 3 to 10 days, and most canker sores disappear within 2 weeks.


There is no way to prevent canker sores.


Treatment focuses on relieving symptoms. Rinsing with a warm-water solution and eating bland foods can minimize discomfort. Anesthetic medications or over-the-counter agents that are placed directly on the sores to coat them also may help.

People with more severe disease may need steroid medications placed on the lesions. These medications significantly shorten the healing time of the ulcers and prevent them from becoming larger. Other possible treatments include placing a medication called chlortetracycline (Aureomycin) on the sores or injecting steroids into the sores. In very severe, disabling cases, your dentist may prescribe oral medication.

When To Call a Professional

Canker sores usually are painful but are not a significant risk to your health. However, if you have severe, recurring canker sores, or if they are becoming worse, consult your dentist or physician. He or she may do tests to look for blood problems such as anemias or deficiencies of iron, folate or vitamin B12. Some research has shown that canker sores improve when these deficiencies are treated. Persistent or large ulcers can also occur as a part of other, more significant, disorders, including inflammatory bowel disease, connective tissue diseases, drug allergies, arthritic disorders, inflammatory skin disorders and cancer.


Most canker sores clear up without treatment and do not leave scars, although they usually return.


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