by Scholten A
(Canker Sores; Aphthous Stomatitis, Recurrent Aphthous Stomatitis)


Aphthous ulcers are painful sores inside the mouth, gums, or lips. They are also called canker sores. The sores can occur one at a time or as a group. Canker sores are temporary and usually not serious.

Canker Sores in the Mouth
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The cause of canker sores is not known. They may be an overreaction of the immune system.

Risk Factors

Canker sores are more common in children and adolescents. They may also run in families.

Things that raise the risk of canker sores are:

  • Injury in the mouth
  • Certain foods, such as:
    • Nuts, chocolate, wheat, or dairy
    • Spicy or acidic foods
  • Some food preservatives
  • Alcohol or fizzy drinks
  • Certain medicines
  • Emotional stress
  • Quitting smoking

Medical conditions that may raise the risk of canker cores are:


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

Some people get canker sores 2 to 3 times per year. Others get sores often. The sores may be painful for 3 to 4 days.

Minor sores may last for a total of 7 to 14 days. Major sores can last for several weeks or even months. They may leave a scar after they heal.


The doctor will ask about your symptoms and health history. A physical exam may be done. The doctor may diagnose the sore based on how it looks.

Tests may be done to rule out other causes. They may be:

  • Biopsy —a small sample of the sore will be tested
  • Blood culture or tests—to look for an infection or other health problem


Most canker sores heal on their own within 1 to 2 weeks. Larger sores may take up to 6 weeks to heal. Treatment is not usually needed.

If canker sores are very painful, the doctor may advise:

  • Oral rinses or gels to ease pain
  • Antibiotic rinses—to treat multiple sores and prevent new sores
  • Pudilan Keyanning toothpaste
  • Steroid rinses—for severe sores
  • Natural therapies, such as beta glucan, camel thorn, and homeopathy
  • Other medicines for recurrent or severe sores, such as:
    • Montelukast
    • Pentoxifylline
    • Cyclosporine
    • Thalidomide


It is not always possible to prevent canker sores. To help reduce the risk:

  • Use relaxation techniques to relieve stress.
  • Chew food carefully—to avoid biting the tongue or cheek.
  • Do not eat foods that are too acidic—or that tend to cause canker sores.
  • Do not use mouth cleaning products and toothpastes with sodium lauryl sulfate.


Family Doctor—American Academy of Family Physicians 

Mouth Healthy—American Dental Association 


Health Canada 

The College of Family Physicians of Canada 


Aphthous stomatitis. EBSCO DynaMed website. Available at: Accessed February 25, 2021.

Bozca BC, Alpsoy E. Experimental therapeutic solutions for Behcet's disease. J Exp Pharmacol. 2021;13:127-145.

Canker sores. Family Doctor—American Academy of Family Physicians website. Available at: Accessed February 25, 2021.

Mortada I, Leone A, et al. Oral manifestations of inflammatory bowel disease. J Biol Regul Homeost Agents. 2017;31(3):817-821.

Revision Information

  • Reviewer: EBSCO Medical Review Board Marcin Chwistek, MD
  • Review Date: 01/2021
  • Update Date: 02/25/2021