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Why am I getting canker sores when I eat oranges?

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The question

When I eat a bunch of oranges (and tomatoes in the summer) I get cankers. What's going on?

The answer

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It sounds like you may be sensitive to acidic foods, which can make you prone to developing canker sores.

Canker sores are small, shallow and sore ulcers that can appear on the soft tissues of the mouth, tongue and gums. Because of their location, they can be painful and make eating and drinking uncomfortable. Canker sores are different than cold sores because they are not contagious, are not associated to herpes virus and do not occur on the surface of your lips.

While it's not entirely clear what causes most canker sores, they are likely due to a combination of factors. Possible triggers for canker sores include emotional stress as well as injury to the tissue in the mouth from irritating food, dental work, ill-fitting dentures or overaggressive brushing. Specific foods, especially those that are acidic such as oranges or tomatoes, can trigger a canker sore or make an existing sore more tender.

In some cases, canker sores can result from underlying health conditions such as impaired immune function or deficiency of certain essential vitamins and minerals, such as vitamin B12, zinc, folic acid or iron. Some gastrointestinal conditions such as celiac disease (gluten intolerance) or inflammatory bowel diseases, such as Crohn's disease or ulcerative colitis, can also lead to ulcers in the mouth.

Canker sores generally last a few days to a week and will heal without treatment. There is no cure for canker sores, so the best way to manage them is to prevent them from occurring. You can reduce frequency by:

  • Avoiding foods that may irritate the mouth such as acidic or spicy foods.
  • Following good oral hygiene. Brush with a soft bristled brush to reduce trauma to the tissues in the mouth, and keep the mouth free of foods that can trigger a sore by brushing and flossing regularly.
  • Treating any underlying medical conditions or vitamin deficiencies.
  • Managing your stress if you notice that the canker sores emerge when you are emotionally drained.

If the sores are unusually large or raw, interfere with swallowing or last longer than three weeks, I recommend seeing your doctor to ensure that there is no underlying medical cause. Your doctor may also be able to suggest some treatment to manage the symptoms such as antimicrobial rinses or steroid cream that can reduce pain and irritation.

Send family doctor Sheila Wijayasinghe your questions at She will answer select questions, which could appear in The Globe and Mail and/or on The Globe and Mail web site. Your name will not be published if your question is chosen.

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The content provided in The Globe and Mail's Ask a Health Expert centre is for information purposes only and is neither intended to be relied upon nor to be a substitute for professional medical advice, diagnosis or treatment.

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