Canker sores: Information, Research, Causes, Symptoms and Treatment

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Aphthous / Mouth Ulcers or Canker Sores


An aphthous ulcer, also known as a canker sore, is a type of oral ulcer, which presents as a painful, shallow open sore inside the mouth, at the base of the gums or upper throat. Unlike cold sores, canker sores don't occur on the surface of your lips and aren't contagious.

20%-40% of the U.S. population suffer from them at some point in their lives; most often affecting people in adolescence and young adulthood. They become less frequent as we get older. Women are more often affected than men, which may be attributed to hormonal changes.

Canker sores and cold sores or fever blisters are often confused for each other; but they have important differences. Fever blisters or cold sores typically appear outside the mouth (most commonly around the lips), while canker sores occur inside the mouth. Also, unlike canker sores, fever blisters are caused by a virus and are extremely contagious.


Canker Sore Types & Symptoms

  • Aphthous ulcers / canker sores ...

are sores inside your mouth - on the tongue, soft palate (the back portion of the roof of your mouth), or inside your cheeks. They usually begin with a tingling or burning sensation at the site of the ulcer prior to its appearance. In a few days, may progress to form a red spot or bump, followed by an open ulcer. The ulcer, may be accompanied by a painful swelling of the lymph nodes below the jaw, which can be mistaken for toothache; another symptom is fever. A sore on the gums may be accompanied by discomfort or pain in the teeth.


    • Minor canker sores (majority of all canker sores) are oval, yellowish or grayish colored lesions with a white center and a red edge or border, between 2-10 mm (up to 1/3 inch) in size. The affected lip may swell. They are painful but clear up within three to 14 days without scarring. It is unusual for them to become infected.

    • Major canker ulcers: Similar appearance to minor aphthous ulcers, but are larger -- more than 10 mm (greater than 1/3 inch) in diameter. They are extremely painful and may take a month or longer to heal. Frequently leave a scar.
  • Herpetiform ulcerations: They resemble herpes infections and occur most frequently in adult females. Characterized by small, numerous, 1–3 mm lesions that form large irregular clusters. They typically last from seven to 10 days and heal without scarring.
  • Additional symptoms may be fever, physical sluggishness and swollen lymph nodes. Canker sores commonly come back. Some people have a few outbreaks a year, while others can have them almost all the time.


Potential Causes / Triggers

  • citrus fruits (e.g. oranges and lemons)
  • lack of sleep; sudden weight loss
  • physical trauma, such as toothbrush abrasions, laceration with sharp or abrasive foods, accidental biting or dental braces can cause aphthous ulcers by breaking the mucous membrane.
  • chemical irritants or thermal injury (hot beverages or foods)
  • stress and/ or hormonal changes
  • food allergies - for example, one recent study showed a strong correlation with allergies to cow's milk
  • immune system reactions. Some patients benefited from eliminating gluten from their diet (Celiac disease)
  • deficiencies in vitamin B12, iron, and folic acid may contribute to their development.
  • Certain types of chemotherapy
  • Less commonly, mouth sores can be a sign of an underlying illness, such as:
    • Crohn's Disease
    • Infection (such as hand-foot-mouth syndrome)
    • Autoimmune diseases (including systemic lupus erythematosus)
    • Bleeding disorders
    • Cancer
    • Weakened immune system
  • Drugs that may cause mouth sores include chemotherapeutic agents for cancer, aspirin, sleep medication (insomnia), gold (for rheumatoid arthritis), penicillin, phenytoin ( for seizures), streptomycin or sulfonamides.


Home Treatments

Pain from a canker sore generally lessens in a few days and the sores usually heal without treatment in about a week or two. However, there are things you can do to relieve discomfort and expedite healing and to prevent future outbreaks.

  • Protect the wound from irritants or further physical trauma inside the mouth
    • such as poorly fitting dentures or braces; a sharp or broken tooth; biting your cheeks, tongue or lips; chewing tobacco; or irritation from gum chewing)
    • avoid spicy or acidic foods that may irritate the sores
    • brush gently
    • potentially consider using a topical ointment as a protective barrier (ask your pharmacist for a recommendation)
  • Apply a thin paste of baking soda and water; or mix 1 part hydrogen peroxide with 1 part water and apply this mixture to the lesions using a cotton swab.
  • Rinse your mouth four times a day with a mixture of two ounces of hydrogen peroxide and two ounces of water; or a combination of four ounces of water mixed with 1 teaspoon (5 milliliters) of salt and 1 teaspoon of baking soda. Swish the mixture in your mouth for about a minute and then spit it out — do not swallow it!
  • Practice proper oral hygiene: Brush with a soft-bristled brush after meals and floss daily to keep your mouth free of foods that might trigger a sore.
  • Dabbing a mixture of equal parts water and hydrogen peroxide directly on the sore, followed by a bit of milk of magnesia, may reduce discomfort and speed healing.
  • Some doctors suggest putting wet black tea bags on sores. Black tea contains tannin, a substance that can relieve pain.
  • Lysine supplements and licorice root reduce the growth of ulcers and aid in speeding the rate of healing
  • Vitamin B12 (1 mg dissolved under the tongue each evening) has been found to be effective in treating recurrent aphthous ulcers, regardless of whether there is a vitamin deficiency present. (Ref.: Volkov I, Rudoy I, Freud T, et al (2009). "Effectiveness of vitamin B12 in treating recurrent aphthous stomatitis: a randomized, double-blind, placebo-controlled trial". J Am Board Fam Med 22 (1): 9–16. doi:10.3122/jabfm.2009.01.080113. PMID 19124628.)
  • According to MedlinePlus Medical Encyclopedia, milk of magnesia is effective against canker sores (aphthous ulcer) when used topically.


Consult your doctor or dentist if ...

  • you are immuno-compromised (for example, patients suffering from HIV; or patients who previously underwent an organ transplant or treatment for cancer)
  • you have unusually large sores or sores that are spreading
  • your sores that last 2 weeks or longer
  • you are suffering from intolerable pain despite avoiding trigger foods and taking over-the-counter pain medication
  • you are having difficulty drinking enough fluids
  • you are experiencing a fever, skin rash or drooling with the appearance of the canker sore(s)
  • the sore begins soon after you started a new medication

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