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Recurrent Aphthous Stomatitis

(Canker Sores; Aphthous Ulcers)


Bernard J. Hennessy

, DDS, Texas A&M University, College of Dentistry

Last full review/revision Jun 2020| Content last modified Jun 2020
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Recurrent aphthous stomatitis (canker sores, or aphthous ulcers) is the presence of small, painful sores (ulcers) inside the mouth that typically begin in childhood and recur frequently.

  • Mouth injury, stress, and some foods may trigger an attack.

  • People feel burning pain, and a day or so later a canker sore develops on the soft tissue of the mouth.

  • Doctors or dentists make the diagnosis based on the pain and the appearance of the canker sores.

  • Treatment is with mouth rinses and sometimes corticosteroids.

Recurrent aphthous stomatitis (RAS) is very common. The cause is unclear but probably involves multiple factors, including disorders or abnormal function of the immune system, exposure to preservatives and toothpaste ingredients, and a genetic predisposition. RAS usually begins in childhood, and 80% of people with RAS are < 30 years old.

People who have RAS get canker sores repeatedly. Some have only one or two canker sores a few times a year. Others have almost continuous outbreaks. Attacks usually decrease in frequency and severity with aging.

Many factors seem to predispose to or trigger attacks, but allergic reactions do not seem to be involved. Such factors include injury to the mouth, stress (for example, a college student may get canker sores during final exam week), and certain foods (particularly chocolate, coffee, peanuts, eggs, cereals, almonds, strawberries, cheese, and tomatoes). People with AIDS often have large canker sores that persist for weeks.

For unknown reasons, pregnant women, people who are taking oral contraceptives, and people who are using tobacco products are less likely to develop canker sores. However, the health risks of tobacco use outweigh any protective effect in preventing canker sores.


Symptoms usually begin with pain or burning, followed in 1 to 2 days by a canker sore. There is never a blister. Pain is severe—far more so than would be expected from something so small—and lasts 4 to 7 days. The canker sores almost always form on soft, loose tissue such as that on the inside of the lip or cheek, on the tongue, on the floor of the mouth, on the soft palate, or in the throat. Sores appear as shallow, round, or oval spots with a yellow-gray center and a red border. Usually, sores are small, about 1/8 to 3/8 inches (less than 1 centimeter) in diameter, and often appear in clusters of two or three. They usually disappear by themselves within 10 days and do not leave scars. Larger sores, about ½ to 1½ inches (less than 3 centimeters) in diameter, are less common. These larger ulcers are irregularly shaped, can take many weeks to heal, and frequently leave scars.

People with a severe outbreak may also have a fever, swollen lymph nodes in the neck, and a generally run-down feeling.


  • A doctor's examination

A doctor or dentist identifies recurrent aphthous stomatitis by its appearance and the pain it causes.


  • Pain relievers

  • Mouth rinses

  • Corticosteroids taken by mouth

Treatment consists of relieving the pain with the same general measures used for other mouth sores (see Mouth Sores and Inflammation : Treatment). In addition, doctors often recommend chlorhexidine mouth rinses. If there are many canker sores, doctors sometimes also recommend a corticosteroid such as dexamethasone applied as a rinse. If there are fewer canker sores, doctors recommend other corticosteroids such as fluocinonide or clobetasol applied as an ointment or mixed in a protective carboxymethylcellulose paste. People who have repeated outbreaks of canker sores may start using the mouth rinse as soon as they feel a sore developing. People using these corticosteroids may develop stomatitis caused by Candida albicans (see Candidiasis : Symptoms).

If the corticosteroids that are applied directly to the affected area do not work, prednisone tablets may be taken by mouth. However, before prescribing a corticosteroid, a doctor must ensure that the person does not have oral herpes simplex infection, which would be made worse by taking corticosteroids. Corticosteroid rinses and tablets are absorbed by the body more than are corticosteroids given in gel form, so the side effects may be a concern (see Corticosteroids: Uses and Side Effects).

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