Aphthous Ulcers

(Canker Sores; Aphthous Stomatitis)

Pronounced: ap-thus ul-sirs


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. Canker sores are generally not serious.

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.

Factors that may increase your chances of canker sores:

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

Medical conditions that may increase your chances of canker cores:


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 2-3 times per year. Others develop sores continually. 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.


You will be asked 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 2 weeks. They may be a sign of cancer.


Canker sores usually heal on their own within 1-2 weeks, although this depends on the size of the sores. Larger sores may take up to 6 weeks to heal. 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:

Oral Pain Relieving Rinses or Gels

An oral rinse may be used every 3 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 4 times per day to numb the area.

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

Oral Antibiotic Rinse

Your doctor may prescribe a liquid antibiotic for multiple sores. It can be used as an oral rinse 4 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:

  • Chew food carefully. This may prevent biting your tongue or cheek.
  • Avoid acidic foods that may promote canker sores. Tomatoes or pineapples are 2 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.


Family Doctor—American Academy of Family Physicians
Mouth Healthy—American Dental Association


The College of Family Physicians of Canada


Aphthous stomatitis. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T114022/Aphthous-stomatitis . Updated December 17, 2013. Accessed December 20, 2017.
Canker sores. Family Doctor—American Academy of Family Physicians website. Available at: https://familydoctor.org/condition/canker-sores. Updated June 2017. Accessed December 20, 2017.
Last reviewed November 2018 by EBSCO Medical Review Board Marcin Chwistek, MD
Last Updated: 12/20/2014

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