What causes canker sores?

The exact cause of canker sores is not known. Genetics play a role. White cells (lymphocytes) in our immune system may affect the lining of the mouth causing these irritating, but harmless, sores. Fatigue, emotional stress, and certain foods can increase the possibility of a canker sore for some people. Even biting the inside of the cheek or tongue or chewing a sharp piece of food may trigger a canker sore.
RealAge
Administration
The exact cause of canker sores or mouth ulcers is unknown. Experts suspect that these painful ulcers may be caused by diet, reactions to medications, or underlying diseases. Sometimes women experience mouth ulcers during their menstrual periods because of the imbalance in hormones. And many people get canker sores during times of stress. 

Some people have a genetic predisposition to mouth ulcers. Also, researchers believe that stress or tissue injury may cause the eruption of canker sores; a minor injury, such as biting the inside of your mouth, may trigger this painful but temporary problem.
Jonathan B. Levine, DMD
Prosthodontics
There are different theories about what triggers aphthous ulcers, more commonly known as canker sores. The fact of the matter is that there are many: depressed immune response, improper nutrition, trauma from dental work. But the one thing these culprits have in common is that they’re all stress-induced in one way or another. If you find yourself getting one canker sore after another, crank up your supply of vitamin B12, avoid hot foods and ask your dentist to prescribe a topical cream to ease the condition.
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Dante A. Gonzales, DMD
Orthodontics & Dentofacial Orthopedics
An Apthous ulcer, more commonly known as a canker sore, is a common recurrent ulcerative condition. The exact cause is unknown. These small sores usually appear in the tissue lining of our mouths. Our own immune system, triggered by a variety of factors, may affect the tissue lining of the mouth. Fatigue, emotional stress, certain food allergies, and mild irritations to the mouth (biting the cheeks, irritations from orthodontic appliances, etc.) may all increase the chances of getting a canker sore. Canker sores are not contagious and usually heal within 7-10 days.
Michael T. Murray, ND
Naturopathic Medicine
Recurrent canker sores appear to be related to trauma; food sensitivities, especially milk and gluten sensitivity; stress; and/or nutrient deficiency. Stress is often a precipitating factor in recurrent canker sores. 
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Canker Sores

Canker Sores

Aphthous stomatitis is a sore that forms inside the mouth, and the most common type is a canker sore. These sores, also called mouth ulcers, are yellow-gray with red rings around them and usually heal in a week or two. Sometimes c...

anker sores are larger or occur in clusters and can take over a month to heal. Treatment is usually with an oral antiseptic and analgesic. Learn more about what affects your risk for canker sores with expert advice from Sharecare.
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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.