Although canker sores are harmless, the pesky ulcers are a source of pain for up to 25 percent of Americans. Usually found on the tongue, the inside of your lips and cheeks or at the base of your gums, canker sores can be triggered by irritation -- accidentally biting your cheek or tongue, for example. But their origin is not always so clear-cut.

Here are tips to help you prevent canker sores in the future, and what you can do now to soothe them:

1. Avoid eating the wrong type of fruit.

A healthy diet filled with immune-system boosting fruits and vegetables is certainly your first line of defense against canker sores. But certain foods -- even some good-for-you fruits -- can exacerbate canker sores. The list includes acidic fruits, such as pineapple, grapefruit and oranges. As for the rest of your diet, stick to milder foods, avoiding spicy dishes and such salty snacks as chips and pretzels.

2. Rethink your vitamin intake.

“One theory is that canker sores are due to a deficiency in some vitamin or nutrient,” says Dr. John C. Comisi, a dentist in Ithaca, N.Y., and a spokesperson for the Academy of General Dentistry. A study published in the Journal of the American Board of Family Medicine found that people with recurrent canker sores had fewer of them after six months of supplementing with 1,000 mg of vitamin B-12. Another study from Okayama University Dental School in Japan found a link between frequent canker sores and low intake of iron, vitamin B-1, calcium and vitamin C.

3. Stress less.

A recent study from the University of Sao Paolo in Brazil discovered a link between stress and recurrent canker sores. “When your body is run down, you’re more susceptible to them,” says Comisi. Take care of yourself by exercising regularly and getting adequate sleep to help guard against canker sores.

4. Give baking soda a chance.

Sure, baking soda can work wonders on your drains and counters -- but did you know it can also offer your mouth relief? Mix it with water until it becomes a paste, then dab it on sore spots several times a day. “It doesn’t taste great, but it’s antimicrobial and soothing,” says Comisi. Rinse off the paste after a few minutes.

5. Try licorice root and other natural remedies.

Many plant-based natural remedies, from aloe gel to goldenseal, can help soothe canker sores. The one with the most research to back it up is licorice-root extract. In a recent study published in the Journal of Contemporary Dental Practice, over-the-counter medicated oral patches containing the ingredient were as effective as a prescription medication for reducing pain and speeding healing of canker sores.

6. Make an appointment.

Canker sores can take two weeks to clear up. If yours last longer, it’s time to seek help from an expert, says Comisi. Your dentist may prescribe a topical medication that includes a numbing agent, such as lidocaine, or a stronger medication, such as an antibiotic rinse or even a corticosteroid ointment. He may also recommend testing by your physician to determine if there is an underlying condition that’s causing the sores, such as Crohn’s disease, celiac disease or some other type of autoimmune disease.

Ella Brooks is a New York City-based health writer and editor. Her articles have appeared in such national women's magazines as Shape, Prevention, Natural Health and Woman's Day.

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