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Recurrent Aphthous Stomatitis

(Canker Sores; Aphthous Ulcers)


Bernard J. Hennessy

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

Reviewed/Revised Feb 2022 | Modified Sep 2022
Topic Resources

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 Human Immunodeficiency Virus (HIV) Infection Human immunodeficiency virus (HIV) infection is a viral infection that progressively destroys certain white blood cells and is treated with antiretroviral medications. If untreated, it can cause... read more Human Immunodeficiency Virus (HIV) Infection 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 of RAS

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.

Diagnosis of RAS

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

Treatment of RAS

  • 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 Topical treatments Treatment Mouth sores and inflammation vary in appearance and size and can affect any part of the mouth, including the lips (see Lip Sores and Inflammation). People may have swelling and redness of the... read more 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 Symptoms of Candidiasis Symptoms Candidiasis is a fungal infection caused by several species of the yeast Candida, especially Candida albicans. The most common type of candidiasis is a superficial infection of... read more 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 Oral infection Herpes simplex virus infection causes recurring episodes of small, painful, fluid-filled blisters on the skin, mouth, lips (cold sores), eyes, or genitals. This very contagious viral infection... read more Oral 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 sidebar Corticosteroids: Uses and Side Effects Corticosteroids: Uses and Side Effects Corticosteroids: Uses and Side Effects ).

More Information

The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

  • Provides information on oral health, including nutrition and guidance on selecting products that carry the American Dental Association's seal of approval. There is also advice on finding a dentist and how and when to see one.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Betasept, Chlorostat, Hibiclens, Oro Clense , Peridex, Periogard, PerioRx , Perisol
AK-Dex, Baycadron, Dalalone, Dalalone D.P, Dalalone L.A, Decadron, Decadron-LA, Dexabliss, Dexacort PH Turbinaire, Dexacort Respihaler, DexPak Jr TaperPak, DexPak TaperPak, Dextenza, DEXYCU, DoubleDex, Dxevo, Hemady, HiDex, Maxidex, Ocu-Dex , Ozurdex, ReadySharp Dexamethasone, Simplist Dexamethasone, Solurex, TaperDex, ZCORT, Zema-Pak, ZoDex, ZonaCort 11 Day, ZonaCort 7 Day
Fluovix, Fluovix Plus, Lidex, Lidex -E, Vanos
Clobetavix, Clobevate, Clobex, Clodan, Cormax, Embeline, Embeline E, Impeklo, Impoyz, Olux, Olux-E, Olux-Olux-E Complete Pack, Temovate, Temovate E, Temovate Scalp, Tovet
Deltasone, Predone, RAYOS, Sterapred, Sterapred DS
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