What Causes Canker Sores?

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  • Last Modified Date: 10 September 2019
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Canker sores are painful sores in the mouth that may be caused by a variety of different agents. It is not always possible to identify their cause, and most physicians will list a number or reasons why they might form. There is no one clear cause, but rather a series of exposures, trauma or predisposing conditions that can result in these sores. It is known that white blood cells attack the mouth in certain spots, and thus those with autoimmune disorders may be more prone to sores.

Some canker sores may be precipitated by trauma to the mouth. Such trauma might include biting the side of one’s cheek, or eating crunchy foods like chips or French bread that might cause a small cut in the mouth. The well-known sourdough bread of San Francisco often sends tourists to the doctor for mouth sores. These small cuts may not develop into sores, but often those with sores can recall some trauma to the mouth prior to development of a sore.

Some canker sores have been linked to toothpastes and mouthwashes that contain sodium lauryl sulfate. This ingredient is included in many brands and is thought to make the mouth dryer, predisposing the unlubricated mouth to form sores. Usually switching to toothpaste that does not contain sodium lauryl sulfate can reduce sores.


Some physicians feel that people with a high degree of stress may be more prone to canker sores. Perhaps higher respiratory rates at this time may cause the mouth to be drier. As well, medications taken for stress, like tranquilizers or sleep aids produce significant dry mouth. When the mouth is not well lubricated, sores are more likely to appear.

Some vitamin deficiencies might cause these sores as wel. Medical researchers have found that low levels of variants of vitamin B and vitamin C can cause sores. Often the B complex vitamins are also used to treat stress or emotional disturbance, so it is hard to say whether the predisposing condition of canker sores is lack of vitamin B or presence of stress, or both.

Food allergies may also cause canker sores. Particularly allergies to acidic foods like tomatoes and oranges may be responsible for developing sores. As well, allergies to milk, grains, and chocolate can be causal factors.

Canker sores might result from viruses or bacterial infection. Those experiencing chemotherapy also have a high risk for these mouth ulcers. Serious viruses like HIV can cause very long-lasting and painful sores, and may indicate a reduction in the ability to fight off infections.

Treatment of canker sores usually depends upon cause, which is not always identifiable. Most doctors recommend finding different toothpaste that does not contain sodium lauryl sulfate. As well, over the counter topical medications for sores can help reduce pain. Where bacterial infection is suspected, antibiotics may be used to resolve sores. Since most sores have no known origin, doctors usually recommend using a topical pain reliever if necessary. One can expect to see the sore resolve within two weeks. Those who have multiple sores, sores that last longer than two weeks, or fever, should see a doctor to rule out infection or illness.


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Post 3

I switched toothpaste to one that does not have sodium lauryl sulfate and I no longer get canker sores. I used to get one or two a month!

Post 2

I would not be surprised since I have FM, and as a result developed other issues - virus-herpes, mouth cankers, multiple food allergies, smell/chemical sensitivity, tremendous daytime fatigue, inability to handle stress, heightened anxiety -- to name a few.

Post 1

Does anyone know of any link between canker sores and fibromyalgia. Particularly a sore on the roof of the mouth?

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