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Cause of Canker Sores

Ben, an Oral Answers reader, recently asked about what really causes canker sores (also known as aphthous ulcers.) He’s heard that sodium lauryl sulfate in toothpaste can cause canker sores, but not everyone who brushes their teeth gets canker sores.

Canker Sore
A canker sore on the posterior roof of the mouth

To be honest, there isn’t any one thing that can cause canker sores in everyone.  However, different things can cause canker sores in different people.

Here’s a list of 10 things that have been shown to cause canker sores in certain people.

10 Things that Cause Canker Sores In Susceptible People

1. Allergies

The book Oral and Maxillofacial Pathology by Neville says, “An antigenic stimulus appears to be the primary initiating factor in the immune-mediated cytotoxic destruction of the mucosa in many patients.”

Basically, it says that the main factor that causes the body to destroy it’s own oral tissues appears to be an allergic response.

There are a LOT of different allergens that have been associated with canker sores.  Here’s a list of the most common ones:

  • Sodium Lauryl Sulfate (SLS), commonly found as a main ingredient in toothpaste
  • Certain medications such as NSAIDS (ibuprofen), beta blockers, and nicorandil
  • A variety of foods, such as:
    • Citrus fruits
    • Strawberries
    • Tomatoes
    • Coffee
    • Gluten (the protein found in wheat products)
    • Dairy products, such as cow’s milk and cheese
    • Nuts
    • Chocolate
    • Food dyes
    • Food flavorings
    • Food preservatives

It’s important to remember that many of the foods listed above do not usually cause canker sores, but they have been found to be trigger foods in certain people. If you think that a certain food is causing your canker sores, you can try to pinpoint which food it is by using the above list and trying an elimination diet.  You will want to talk to your doctor about your concerns to get additional information before attempting to eliminate certain foods altogether.

2. Stress

Stress is a major cause of canker sores.  It is presumed that since stress weakens the body’s immune system that it makes it more susceptible to canker sores.

3. Trauma

Trauma has also been associated with canker sores.  Anytime the barrier over the deeper tissues inside your mouth is broken, there is a higher risk for canker sores in certain people.  The trauma can be caused by a variety of things, such as sharp foods like chips and crackers, biting, braces or hard=bristled toothbrushes.

4. Genetics

Your family history can play a big role in whether or not you get canker sores.  In fact, if both of your parents get canker sores, there’s a 90% chance that you will get them too!

Joseph A. Regezi, in his oral pathology book states, “Family history represents a risk factor. Over 40% of affected patients have a first-degree relative who is also affected by aphthous ulcers. There is a 90% degree of risk when both parents are affected.”

5. Compromised Immune System

Some people who have problems with their immune system have many canker sores.  For example, people with AIDS (Acquired Immunodeficiency Syndrome) frequently get aphthous ulcers.

6. Infectious Organisms

Certain organisms have also been implicated in causing canker sores in certain people.  Some examples of organisms that are associated with canker sores are:

  • Certain forms of streptococci
  • Helicobacter pylori
  • Herpes simplex virus
  • Varicella-Zoster virus (chicken pox)
  • Adenovirus
  • Cytomegalovirus

7. Nutritional Deficiencies

Nutritional deficiencies have been shown to be correlated with canker sores.  Shortages of the following vitamins and minerals are suspect:

  • Iron
  • Folic Acid
  • Zinc
  • The “B” Vitamins (Vitamin B1, B2, B6, and B12)

8. Stopping Smoking

When you smoke, the tissue lining the inside of your mouth gets slightly thicker.  Quitting smoking thins the lining inside of your mouth and makes you more susceptible to canker sores.

This doesn’t mean that you should smoke to avoid canker sores!  Smoking has many more serious negative effects on your oral health.  For example, smoking has been linked to oral cancer and smokers in general have less teeth than non-smokers.  So it is still a great idea to quit smoking if you currently do!

9. Hormones

Hormones can also affect whether or not you get canker sores.  The book Oral and Maxillofacial Pathology by Neville says, “In a small subset of female patients, a negative association was reported between the occurrence of [canker sores] and the luteal phase of the menstrual cycle—a period of mucosal proliferation and keratinization.”

The luteal phase of your menstrual cycle begins right after you ovulate (approximately day 14) and ends on the day you get your next period.  When the tissue inside your mouth gets thicker (i.e. – more keratin forms) then you see a decrease in the amount of canker sores.

10. Blood Abnormalities

Certain blood abnormalities, such as cyclic neutropenia have also been implicated in canker sores.  Regezi’s Oral Pathology textbook states the following (I bolded the part that deals with canker sores):

“Cyclic neutropenia, a rare blood dyscrasia, is manifested as severe cyclic depletions of neutrophils from the blood and marrow, with a mean cycle, or periodicity, of about 21 days…Fever, malaise, oral ulcers, cervical lymphadenopathy, and infections may appear during neutropenic episodes.”


There are a variety of things that can cause canker sores.  However, you may notice that nothing I mentioned above applies to you and you still have canker sores.  This is because we still don’t know everything that causes canker sores.  Researchers are still working to understand the exact reasons why some people get them and some people don’t.

Do you get canker sores?  Have you noticed that they are caused something that I didn’t mention above?  I’d love to hear your comments and questions in the comments section below.  Thanks for reading!