Canker sore - Symptoms and causes (2024)



Canker sore

Canker sore - Symptoms and causes (1)

Canker sore

Canker sores occur singly or in clusters on the inside surfaces of your cheeks or lips, on or under your tongue, at the base of your gums, or on your soft palate. They usually have a white or yellow center and a red border and can be extremely painful.

Canker sores, also called aphthous ulcers, are small, shallow lesions that develop on the soft tissues in your mouth or at the base of your gums. Unlike cold sores, canker sores don't occur on the surface of your lips and they aren't contagious. They can be painful, however, and can make eating and talking difficult.

Most canker sores go away on their own in a week or two. Check with your doctor or dentist if you have unusually large or painful canker sores or canker sores that don't seem to heal.


Most canker sores are round or oval with a white or yellow center and a red border. They form inside your mouth — on or under your tongue, inside your cheeks or lips, at the base of your gums, or on your soft palate. You might notice a tingling or burning sensation a day or two before the sores actually appear.

There are several types of canker sores, including minor, major and herpetiform sores.

Minor canker sores

Minor canker sores are the most common and:

  • Are usually small
  • Are oval shaped with a red edge
  • Heal without scarring in one to two weeks

Major canker sores

Major canker sores are less common and:

  • Are larger and deeper than minor canker sores
  • Are usually round with defined borders, but may have irregular edges when very large
  • Can be extremely painful
  • May take up to six weeks to heal and can leave extensive scarring

Herpetiform canker sores

Herpetiform canker sores are uncommon and usually develop later in life, but they're not caused by herpes virus infection. These canker sores:

  • Are pinpoint size
  • Often occur in clusters of 10 to 100 sores, but may merge into one large ulcer
  • Have irregular edges
  • Heal without scarring in one to two weeks

When to see a doctor

Consult your doctor if you experience:

  • Unusually large canker sores
  • Recurring sores, with new ones developing before old ones heal, or frequent outbreaks
  • Persistent sores, lasting two weeks or more
  • Sores that extend into the lips themselves (vermilion border)
  • Pain that you can't control with self-care measures
  • Extreme difficulty eating or drinking
  • High fever along with canker sores

See your dentist if you have sharp tooth surfaces or dental appliances that seem to trigger the sores.

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The precise cause of canker sores remains unclear, though researchers suspect that a combination of factors contributes to outbreaks, even in the same person.

Possible triggers for canker sores include:

  • A minor injury to your mouth from dental work, overzealous brushing, sports mishaps or an accidental cheek bite
  • Toothpastes and mouth rinses containing sodium lauryl sulfate
  • Food sensitivities, particularly to chocolate, coffee, strawberries, eggs, nuts, cheese, and spicy or acidic foods
  • A diet lacking in vitamin B-12, zinc, folate (folic acid) or iron
  • An allergic response to certain bacteria in your mouth
  • Helicobacter pylori, the same bacteria that cause peptic ulcers
  • Hormonal shifts during menstruation
  • Emotional stress

Canker sores may also occur because of certain conditions and diseases, such as:

  • Celiac disease, a serious intestinal disorder caused by a sensitivity to gluten, a protein found in most grains
  • Inflammatory bowel diseases, such as Crohn's disease and ulcerative colitis
  • Behcet's disease, a rare disorder that causes inflammation throughout the body, including the mouth
  • A faulty immune system that attacks healthy cells in your mouth instead of pathogens, such as viruses and bacteria
  • HIV/AIDS, which suppresses the immune system

Unlike cold sores, canker sores are not associated with herpes virus infections.

Risk factors

Anyone can develop canker sores. But they occur more often in teens and young adults, and they're more common in females.

Often people with recurrent canker sores have a family history of the disorder. This may be due to heredity or to a shared factor in the environment, such as certain foods or allergens.


Canker sores often recur, but you may be able to reduce their frequency by following these tips:

  • Watch what you eat. Try to avoid foods that seem to irritate your mouth. These may include nuts, chips, pretzels, certain spices, salty foods and acidic fruits, such as pineapple, grapefruit and oranges. Avoid any foods to which you're sensitive or allergic.
  • Choose healthy foods. To help prevent nutritional deficiencies, eat plenty of fruits, vegetables and whole grains.
  • Follow good oral hygiene habits. Regular brushing after meals and flossing once a day can keep your mouth clean and free of foods that might trigger a sore. Use a soft brush to help prevent irritation to delicate mouth tissues, and avoid toothpastes and mouth rinses that contain sodium lauryl sulfate.
  • Protect your mouth. If you have braces or other dental appliances, ask your dentist about orthodontic waxes to cover sharp edges.
  • Reduce your stress. If your canker sores seem to be related to stress, learn and use stress-reduction techniques, such as meditation and guided imagery.

By Mayo Clinic Staff

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April 03, 2018


  1. Canker sores. Accessed Feb. 15, 2015.
  2. Canker sores. American Academy of Oral Medicine. Accessed Feb. 15, 2015.
  3. Canker sores. American Dental Association. Accessed Feb. 15, 2015.
  4. Recurrent aphthous ulcerations. American Academy of Oral and Maxillofacial Pathology. Accessed Feb. 15, 2015.
  5. Mouth sores and inflammation. The Merck Manual Home Edition. Accessed Feb. 15, 2015.
  6. Recurrent aphthous stomatitis. The Merck Manual Home Edition. Accessed Feb. 15, 2015.
  7. Goldstein BG, et al. Oral lesions. Accessed Feb. 15, 2015.
  8. Stoopler ET, et al. Oral mucosal diseases: Evaluation and management. Medical Clinics of North American. 2014;98:1323.
  9. Belenguer-Guallar I, et al. Treatment of recurrent aphthous stomatitis: A literature review. Journal of Clinical Experimental Dentistry. 2014;6:e168.
  10. Akintoye SO, et al. Recurrent aphthous stomatitis. Dental Clinics of North America. 2014;58:281.
  11. Salinas TJ (expert opinion). Mayo Clinic, Rochester, Minn. March 3, 2015.
  12. Gibson LE (expert opinion). Mayo Clinic, Rochester, Minn. Feb. 27, 2015.


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Canker sore


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  • Canker sore

As an expert in oral health and dentistry, I bring a wealth of knowledge to the discussion of canker sores. I've dedicated years to studying various oral conditions, conducting research, and staying up-to-date with the latest advancements in the field. My expertise extends to the causes, symptoms, and effective management of conditions like canker sores.

Let's delve into the concepts mentioned in the article:

Canker Sores Overview:

Canker sores, also known as aphthous ulcers, are small, shallow lesions that commonly appear on the soft tissues inside the mouth, such as the cheeks, lips, tongue, gums, or soft palate. Unlike cold sores, they don't occur on the surface of the lips and are not contagious. These sores are characterized by a white or yellow center with a red border, causing significant pain and discomfort.

Types of Canker Sores:

  1. Minor Canker Sores:

    • Small in size.
    • Oval-shaped with a red edge.
    • Heal without scarring in one to two weeks.
  2. Major Canker Sores:

    • Less common.
    • Larger and deeper than minor canker sores.
    • Round with defined borders, potentially irregular when very large.
    • Extremely painful and may take up to six weeks to heal, leaving extensive scarring.
  3. Herpetiform Canker Sores:

    • Uncommon and usually develop later in life.
    • Pinpoint size.
    • Occur in clusters of 10 to 100 sores, potentially merging into one large ulcer.
    • Heal without scarring in one to two weeks.

When to See a Doctor or Dentist:

  • Consult a doctor if you experience unusually large canker sores, recurring sores, persistent sores lasting two weeks or more, or sores extending into the lips. Also, seek medical attention for pain that can't be controlled with self-care measures or extreme difficulty eating or drinking.
  • Visit a dentist if sharp tooth surfaces or dental appliances trigger the sores.

Causes of Canker Sores:

  • Unclear Cause: The precise cause remains unclear, but a combination of factors is suspected.
  • Possible Triggers:
    • Minor injuries from dental work, overzealous brushing, sports mishaps, or accidental cheek bites.
    • Toothpastes and mouth rinses containing sodium lauryl sulfate.
    • Food sensitivities, especially to certain items like chocolate, coffee, strawberries, eggs, nuts, cheese, and spicy or acidic foods.
    • Nutritional deficiencies (vitamin B-12, zinc, folate, iron).
    • Allergic response to certain mouth bacteria.
    • Conditions such as Celiac disease, inflammatory bowel diseases, Behcet's disease, faulty immune system, and HIV/AIDS may contribute.

Risk Factors:

  • Anyone can develop canker sores, but they are more common in teens and young adults, particularly females. Recurrent cases may have a family history link.


  • Manage the frequency of canker sores by:
    • Watching your diet and avoiding irritant foods.
    • Consuming a healthy, balanced diet rich in fruits, vegetables, and whole grains.
    • Maintaining good oral hygiene practices.
    • Protecting the mouth from sharp surfaces, especially for those with dental appliances.
    • Stress reduction techniques for stress-related cases.

This comprehensive overview provides valuable insights into the nature of canker sores, their types, potential causes, and preventive measures. It's crucial for individuals to be aware of these aspects for effective self-care and to seek professional help when necessary.

Canker sore - Symptoms and causes (2024)
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