What Are Canker Sores (Mouth Ulcer) and Their Symptoms?

Canker sores, also known as mouth ulcers, are small, shallow lesions in the mouth's lining.1 They can develop on the tongue, lip, gum, mouth roof, inside of cheeks, or under the tongue.2 Canker sores can be painful and can make eating, drinking, and talking uncomfortable. There are three major types of canker sores:

  • Minor Canker Sores:

    Minor canker sores are the most common type and are typically small (less than 1 centimeter in diameter), oval-shaped, and heal without scarring in one to two weeks. They feature a white or yellowish center surrounded by a red border.2,3

  • Major Canker Sores:

    Major canker sores are larger (over 1 centimeter in diameter) and deeper than minor canker sores, often with a raised or irregular border. They can be extremely painful and take weeks to months to heal and may leave a scar.2,3

  • Herpetiform Canker Sores:

    Herpetiform canker sores can look like a herpes outbreak, but the herpes virus is not involved. They are clusters of tiny ulcers that can merge into one large ulcer. They have irregular edges and heal without scarring in about one to two weeks. These are more common in older adults.2,3

  1. How Long Do Canker Sores Last?

    Canker sores or mouth ulcers typically last for one to two weeks. The duration can depend on the type of canker sore. Minor or herpetiform canker sores often heal within one to two weeks. Major canker sores can take up to six weeks to heal.2,3

  2. Are Canker Sores Contagious?

    Canker sores are not contagious. Canker sores arise due to various factors, including stress, hormonal changes, certain food sensitivities, or minor injuries to the mouth, rather than being caused by an infectious agent.3,4

  3. Canker Sores vs. Cold Sores

    Cold sores, also known as fever blisters, result from an infection with herpes simplex virus. Unlike canker sores, cold sores can be spread through close personal contact, including kissing and sharing of personal items. Cold sores are characterized by fluid-filled blisters that can form clusters, often appearing on the lip or around the mouth.1,4 Canker sores, on the other hand, only develop inside the mouth and aren’t contagious.4

What Causes Canker Sores or Mouth Ulcers?

While the exact cause of canker sores is unknown,1 many factors can trigger the development:

  • Nutrient deficiencies: A diet lacking in vitamin B12, zinc, folic acid or iron may lead to increased occurrence of sores.1,3,5
  • Stress and anxiety: Emotional stress and anxiety can manifest physically, with canker sores being a common symptom during periods of heightened emotional turmoil.1,3,5
  • Damaged gums or oral tissues: Dental procedures, vigorous brushing, poorly fitted dental appliances, or accidental cheek bites, can all damage delicate mouth tissues, making them prone to the development of canker sores.1,3,5
  • Food sensitivities: Sensitivity to certain foods such as chocolate, coffee, strawberries, eggs, nuts, cheese, and spicy or acidic foods may cause canker sores.3,6

How to Prevent or Get Rid of Canker Sores

Preventing and managing canker sores involves a combination of attentive oral care, lifestyle changes, and dietary adjustments. Here are some effective strategies or home remedies for canker sores:

  1. Use a Soft-Bristled Toothbrush

    A soft-bristled brush is gentle on the mouth tissue, reducing the risk of injury and irritation which could trigger canker sores.6 Additionally, if canker sores are already present, using a soft brush can prevent further exacerbation, allowing for faster healing.3

  2. Practice Good Oral Hygiene

    Maintaining a good oral hygiene could help minimize the risk of canker sores and maintain optimal oral health. Brush your teeth gently twice daily, especially after meals, and floss once a day to remove lingering bacteria and potential food triggers.3

  3. Foods and Drinks to Avoid with Canker Sores

    Managing and preventing canker sores often involves being cautious about certain food and drink choices. Here are examples of items you might consider limiting:3


    • Spicy Foods: Examples include hot sauces, chili peppers, and certain curries.
    • Salty Foods: Such as pretzels, salted nuts, and some snack chips.
    • Acidic Foods and Drinks: Items like citrus fruits (e.g., oranges and lemons), tomatoes, pineapples, and vinegar can be problematic. Additionally, some beverages, like sodas or specific fruit juices, fall into this category.


    Diet plays a pivotal role in oral health. For more on how diet impacts oral health, visit Listerine's guide on foods and gum disease.

  4. Consider Nutritional Supplements

    Canker sores may be linked to nutritional deficiencies in vitamin B12, zinc, folic acid, and iron.1,3,5 By supplementing these nutrients, one can potentially speed healing and reduce the frequency and severity of canker sores.10 Talk to your doctor before starting any supplements for the prevention or treatment of canker sores.

When to Visit a Doctor for Your Mouth Ulcers

If a canker sore or mouth ulcer persists for more than two weeks, keeps coming back, grows in size, or is accompanied by extreme pain, high fever, or difficulty swallowing, it's essential to seek medical attention.3 A healthcare professional may conduct diagnostic tests to rule out underlying health conditions and could prescribe topical treatments, oral medications, or specialized mouthwashes to expedite healing and alleviate pain associated with the ulcer.11

1 - Cleveland Clinic. Canker Sore (Aphthous Ulcer): What It Is, Causes & Treatment. Cleveland Clinic. Retrieved from: https://my.clevelandclinic.org/health/diseases/10945-canker-sores
2 - The American Academy of Oral Medicine. Canker Sores. Retrieved from: https://www.aaom.com/index.php%3Foption=com_content&view=article&id=82:canker-sores&catid=22:patient-condition-information&Itemid=120
3 - Mayo Clinic. Canker sore - Symptoms and causes. Mayo Clinic. Retrieved from: https://www.mayoclinic.org/diseases-conditions/canker-sore/symptoms-causes/syc-20370615
4 - Cleveland Clinic. Cold Sore: Causes, Treatment & Prevention. Retrieved from: https://my.clevelandclinic.org/health/diseases/21136-cold-sores
5 - Mount Sinai Health System. Canker sore Information | Mount Sinai - New York. Mount Sinai Health System. Retrieved from: https://www.mountsinai.org/health-library/diseases-conditions/canker-sore
6 - Cedars-Sinai. Everything You Ever Wanted to Know About Canker Sores. Cedars-Sinai. Retrieved from: https://www.cedars-sinai.org/blog/canker-sores.html
7 - NHS. Mouth ulcers. nhs.uk. Published October 18, 2017. Retrieved from: https://www.nhs.uk/conditions/mouth-ulcers/
8 - The American Academy of Oral Medicine. Canker Sores - Treatment. Retrieved from: https://maaom.memberclicks.net/index.php%3Foption%3Dcom_content%26view%3Darticle%26id%3D86:canker-sores-treatment%26catid%3D22:patient-condition-information%26Itemid%3D120
9 - Canker sore - Diagnosis and treatment - Mayo Clinic. Retrieved from: https://www.mayoclinic.org/diseases-conditions/canker-sore/diagnosis-treatment/drc-20370620
10 - Belenguer-Guallar I, Jimenez-Soriano Y, Claramunt-Lozano A. Treatment of recurrent aphthous stomatitis. A literature review. J Clin Exp Dent. Published online 2014:e168-74. doi:10.4317/jced.51401
11 - familydoctor.org. Canker Sores. familydoctor.org. Retrieved from: https://familydoctor.org/condition/canker-sores/