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What Are Canker Sores?

My son gets canker sores often. The other day he asked me what they were and I didn't have a good answer. Can you help?

– Matt

Canker sores are ulcers that develop inside the mouth. Although doctors don't fully understand why canker sores appear, they do know they often occur following an injury, like when a person has bitten his tongue or cheek. Things like stress, menstrual periods, and food allergies can also trigger canker sores.

Canker sores can cause pain or burning that starts to go away within several days. Most canker sores can be treated by applying ice or over-the-counter ointments to relieve pain. It may help to avoid food and drinks that have a lot of acid, such as orange juice, or that are sharp, like potato chips, when a canker sore is present.

We regret that we can't reply to any email inquiry. Although we can't reply personally, you may see your question posted to this page in the future. If you're looking for medical advice, a diagnosis, or treatment, consult your doctor or other qualified medical professional. If this is an emergency, contact emergency services in your area.

Reviewed by: Larissa Hirsch, MD
Date reviewed: June 2007