Q: I'm getting more canker sores than I used to. What could be causing that and what’s the best way to treat these sores?

A: Canker sores are painful lesions that can develop inside your mouth—on your tongue and the linings of your cheeks, lips, and even your throat, according to the National Institute of Dental and Craniofacial Research. More than half of us experience a canker sore at one point or another, says the American Academy of Oral Medicine, and the problem may recur over the years.

What Can Cause a Canker Sore?

Canker sores can occur as a result of injury to your mouth, reactions to foods such as chocolate and peanuts, your genes, and your stress level. Even a common toothpaste ingredient, called sodium lauryl sulfate, can trigger the painful mouth sores.

Noncontagious, canker sores begin as small red swellings, which open up soon after they develop. After this, a thin, pale membrane edged by red generally covers them until they heal.

How to Handle Canker Sore Pain

There’s no cure for these annoying sores, but they usually go away on their own within a couple of weeks. In the meantime, you can ease the discomfort by rinsing your mouth with mild salt water or by dabbing a mixture of half hydrogen peroxide, half water on the sore, then applying a little bit of Milk of Magnesia (magnesium hydroxide) to the area. Swishing a 50/50 mixture of Milk of Magnesia and liquid diphenhydramine (Benadryl Allergy and generic) in your mouth for a minute, then spitting it out, may also help.

If the sores are very painful or slow to heal, your doctor can prescribe a pain-relieving mouthwash containing chlorhexidine gluconate and/or steroids (as either an ointment or pill).

See your doctor if your canker sores are large (in severe cases, the sores may be close to a half-inch in diameter), last longer than two weeks, crop up more than three times a year, keep you from eating and drinking, or if you also have a fever, skin rash, headache or diarrhea. Sometimes, medical conditions such as inflammatory bowel disease and celiac disease can trigger outbreaks.