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Aphthous Ulcers

(Canker Sores; Aphthous Stomatitis)

Pronounced: ap-thus ul-sirs
En Español (Spanish Version)

Definition | Causes | Risk Factors | Symptoms | Diagnosis | Treatment | Prevention


Aphthous ulcers are also known as canker sores. They are painful, temporary sores that may occur anywhere in the mouth. The sores can occur one at a time or as a group. Although canker sores are not serious, other mouth sores may be. If you suspect you have this condition, make an appointment to see your doctor.

Canker Sores in the Mouth

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No one knows exactly what causes canker sores. They are thought to result from an overreaction of the immune system.

Canker sores are not a form of the herpes virus. Unlike herpes, canker sores cannot spread from one person to another.

Risk Factors

Canker sores tend to occur more often in women than in men. The tendency for these sores may also run in families.

The following may increase your chance of a canker sore:

  • Stress or trauma in the mouth, such as biting the tongue, trauma from falls, or toothbrushes
  • Certain foods (especially acidic foods, such as tomatoes and pineapples)
  • Changes in hormone levels

Medical conditions that may increase your chance of canker cores include:


Canker sores can be various sizes. They typically occur on the inner surface of the cheeks and lips, and on or under the tongue. Canker sores are an open, shallow grayish sore. It may have a slightly raised, yellowish-white border that is surrounded by a red border.

Some people get canker sores two or three times per year. Others develop sores continually one after another. Usually the most painful phase is the first 3-4 days. The sores begin to heal after 3- 4 days.

Minor sores may last for a total of 7-14 days. They often heal without scarring. Major sores can last for several weeks or even months. They may leave a scar after they heal.


Your doctor will ask about your symptoms and medical history. A physical exam will be done. Your doctor will most likely be able to tell the difference between a canker sore or more serious mouth sore by looking at it. To rule out other problems your doctor may do the following:

  • Biopsy—a small sample of the sore will be sent to a lab for closer examination
  • Blood culture or tests—to look for signs of an infection or other systemic health conditions

It is especially important to examine mouth sores that do not heal within two weeks. They may be a sign of cancer.


Canker sores usually heal on their own within 1-2 weeks. Treatments for these sores are not usually necessary.

If your canker sore is especially painful or is taking a long time to heal, your doctor may recommend the following:

An oral rinse may be used every three hours or before meals. This provides short-term relief from pain. In addition, anti-pain oral gels can be applied directly on the sores. It may be used about four times per day to numb the area.

These products can be found in pharmacy stores. Prescriptions are not needed.

Your doctor may prescribe a liquid antibiotic for multiple sores. It can be used as an oral rinse four times daily for 10 days. The liquid can coat the ulcers and prevent new sores from forming. Sometimes, this treatment can cause an oral infection called candidiasis (thrush). Thrush can be easily treated.

Steroids may be recommended for severe outbreaks. The steroid is usually given as a liquid oral rinse. Steroids help reduce swelling in the mouth caused by severe sores.


It is not always possible to prevent canker sores. To help reduce your chances of canker sores, take the following steps:

  • Chew food carefully. This may prevent biting your tongue or cheek.
  • Avoid acidic foods that may promote canker sores. Tomatoes or pineapples are two foods that may cause problems.
  • Talk to your doctor about how to get enough iron, vitamin B12, or folate in your diet. Low levels of these nutrients may contribute to canker sores.

American Academy of Family Physicians


American Dental Association



Canadian Family Physician



Aphthous stomatitis. EBSCO DynaMed website. Available at: https://dynamed.ebscohost.com/about/about-us. Updated August 31, 2012. Accessed December 7, 2012.

Beers MH, Berkow R. The Merck Manual. 17th ed. West Point, PA: Merck and Co; 1999.

Canker sores. American Family Physicians Family Doctor website. Available at: http://familydoctor.org/familydoctor/en/diseases-conditions/canker-sores.html. Accessed December 7, 2012.

Last reviewed November 2012 by Michael Woods, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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