Why Do I Keep Getting Canker Sores in My Mouth?

Reviewed on 12/7/2020

What are canker sores?

Canker sores are small open ulcers that usually appear on the inside of your mouth. Causes include stress, hormonal changes, nutritional deficiencies, foods and other more. They usually heal on their own and don't require any treatment but can sometimes point toward an underlying issue.
Canker sores are small open ulcers that usually appear on the inside of your mouth. Causes include stress, hormonal changes, nutritional deficiencies, foods and more.

Canker sores (aphthous ulcers) are small open ulcers that show up in your mouth, typically inside the lip or cheek. They’re white or yellow in color and are often surrounded by red, inflamed tissue

These painful sores are among the most common oral conditions, and they affect almost half of all people. There are actually three main types of canker sore:

  • Minor aphthous stomatitis, which is the most common type, are small ulcers that heal within a week.
  • Major aphthous stomatitis, which is a more severe type, are larger and more painful. They heal within two weeks and often leave scars.
  • Herpetiform aphthous stomatitis, which occurs in less than 5% of people who have canker sores, is a cluster of tiny sores.

In many cases, canker sores heal on their own and don’t require any treatment. In some instances, however, they can point toward an underlying issue that may require medical treatment.

Signs and symptoms of canker sores

One of the most obvious signs of a canker sore is a small, painful yellow or white ulcer inside of your lip or cheek. For some, the sore appears on the gums. These sometimes get confused with cold sores. There are a few things that can help you to tell the difference.

One of the biggest differences between cold sores and canker sores is that cold sores appear on the outside of the mouth, usually around the lips. In some instances, they may show up on the roof of your mouth or tongue. Canker sores always appear inside the lips or cheeks. Another major difference between the two is that canker sores aren’t contagious, while cold sores are. 

Other signs and symptoms of canker sores include:

Tingling or burning inside your mouth

You may notice a tingling or burning feeling inside of your mouth before the canker sore appears. 


While it’s not always the case, some people develop a fever when they get a canker sore. A high fever can point toward a more serious issue.


Some people with canker sores may feel tired

Swollen lymph nodes

While not as common as some of the other symptoms, swollen lymph nodes may come along with a canker sore. The swelling may mean that there’s another issue going on, and you should schedule an appointment with your doctor

Causes of canker sores

Several different things can lead to a canker sore. Some of the most common include:


The connection between stress and canker sores isn’t well-understood, but studies do suggest that increased levels of stress can cause the ulcers to develop . 

Hormonal changes

Fluctuations in hormones may cause canker sores. Women who are prone to them may notice that the ulcers appear a few days before their period and go away after it’s done. 

Nutritional deficiencies

You might develop canker sores if your body is lacking certain nutrients. Some studies show that low levels of B vitamins can increase the risk of these painful ulcers. Other studies show that low iron levels may contribute to canker sores. 

Certain types of foods

Acidic foods, such as lemons, limes, oranges, tomatoes, strawberries, and more, can sometimes cause a canker sore to develop. You may also develop canker sores if you are sensitive to certain types of foods, such as chocolate, coffee, eggs, or anything spicy. 

Certain ingredients in toothpaste

Sodium lauryl sulfate, a common ingredient in toothpaste and mouthwash, can cause canker sores. Studies show people who use oral care products with this ingredient are more likely to have them.

Mouth injuries

Injuries to the soft tissues inside of your mouth — such as brushing too hard, biting your cheek, rubbing from braces, or ill-fitting dentures — can sometimes cause a canker sore to form. 

Autoimmune diseases

Canker sores may develop as a side effect of an autoimmune disease. The ulcers are linked to many conditions, such as:

Diagnosing canker sores

You don’t need to undergo any tests to diagnose a canker sore. Your doctor or dentist can identify them by looking at them. If your doctor believes that the ulcers are occurring as a result of an underlying condition, however, you may undergo other tests to determine what that issue is.

Treatments for canker sores

In many cases, canker sores go away on their own without treatment. Large or painful canker sores that last longer than two weeks, however, may need medical care. Some common treatment options for these ulcers include:

If your canker sores are the result of an underlying health condition, your doctor will provide recommendations to treat that issue. 


Mouth Problems: TMJ, Canker Sores, Painful Gums and More See Slideshow

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The American Academy of Oral Medicine: "Canker Sores."

Penn Medicine: "Cold Sores Vs. Canker Sores: What Are They and How Do I Get Rid of 'Em?"

Clinics: "Psychological Stress and Recurrent Aphthous Stomatitis."

Mouth Healthy: "Hormones and Dental Health: What Every Woman Needs to Know."

Journal of Oral Pathology & Medicine: "Recurrent Aphthous Ulceration: Vitamin B1, B2, and B6 Status and Response to Replacement Therapy."

Oral Surgery, Oral Medicine, and Oral Pathology: "Hematological Status in Recurrent Aphthous Stomatitis Compared with Other Oral Disease."

Cleveland Clinic:"Canker Sores."

Acta Odontologia Scandinavica: "Sodium Lauryl Sulfate and Recurrent Aphthous Ulcers. A Preliminary Study."

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