Cause of canker sores unknown, but simple measures can provide relief

Cause of canker sores unknown, but simple measures can provide relief

The Medicine Cabinet: Ask the Harvard Experts 

Q: I get canker sores about two to three times per year. Generally there is just one, but sometimes I have a couple at the same time. What causes them? Can they be prevented?

A: A canker sore is a painful ulcers on the inside of the cheek or tongue. Doctors call them aphthous ulcers.

A canker sore can be very painful, especially when eating spicy or acidic foods. The symptoms last up to 10 days and will go away without any treatment. But they often recur a few times a year or even every month or two.

Canker sores are common, affecting up to 40% of the population. In most cases, there are only one or two ulcers at a time.

Despite years of research, no exact cause for aphthous ulcers has been found. Most likely there is a genetic predisposition to getting them, as they seem to run in families. The immune system almost surely plays a role. But what triggers the immune reaction is unknown.

Aphthous ulcers can be a symptom of systemic conditions. Symptoms that might suggest that they are complex canker sores include frequent and persistent mouth ulcers, genital ulcers, fever, joint pain and a rash.

For common canker sores, there are no proven strategies to prevent them. Emotional stress or trauma like biting your cheek or lip can sometimes be a trigger.

Aphthous ulcers can occur in people with celiac disease if they ingest gluten. And people who have gluten sensitivity and recurrent canker sores might see if avoiding gluten makes a difference.

In general, eating a healthy, well balanced diet to be certain that you are getting all the vitamins and nutrients you need makes sense. But there is no evidence that taking vitamin or mineral supplements helps prevent aphthous ulcers from recurring.

Many topical agents can help with pain relief. For example, mix equal parts of Milk of Magnesia and diphenhydramine (Benadryl) liquid. Swish a teaspoon of the mixture in your mouth for 30 second to 60 seconds, then spit it out. Repeat it every three to four hours.

For stronger relief, your doctor or dentist may prescribe a local anesthetic, such as viscous lidocaine. For more stubborn canker sores, a small amount of a prescription corticosteroid can be applied directly to the ulcers.

(Howard LeWine, M.D. is an internist at Brigham and Women’s Hospital in Boston and assistant professor at Harvard Medical School. For additional consumer health information, please visit