They are one of medicine's little mysteries. Doctors can't explain what causes canker sores and why some people are rarely bothered by them while others suffer frequently.
Sometimes a canker sore appears for no apparent reason. Other times you bite your cheek and you just know that the next day the spot will be tender and swollen.
The medical term for canker sores is aphthous ulcers. People sometimes confuse them with cold sores or fever blisters, common names for herpes simplex lesions on the lips. But canker sores appear inside the mouth and are not associated with herpes. A bad case can make it hard for a person to eat or talk.
A few months ago we heard from a retired physician troubled with recurrent canker sores. His mouth was so tender he had trouble chewing his food, and the medicines his doctor and dentist had given him were not working.
Around the same time, D.W., who listens to our radio program, contacted us to tell us that his mother, a dental assistant during the Depression, had seen sauerkraut juice work wonders on canker sores. Swishing about a tablespoon in the mouth several times a day and then swallowing the juice seemed to help the lesions heal more quickly.
When we suggested this humble home remedy, the doctor was skeptical, but he was desperate enough to try anything. To his surprise, the canker sores cleared up. Although Temovate, the powerful steroid gel his physician prescribed, got some of the credit, sauerkraut juice has held his canker sores at bay since then.
We have received dozens of other recommendations on home remedies for canker sores. One woman wrote: "Many years ago when I was in college, I developed a mouthful of painful canker sores just as Easter vacation began. I couldn't eat, only drink milkshakes through a straw.
"The pharmacist first offered gentian violet and citrate of magnesia, but that didn't work. Then he told Mother to put a teaspoon of Massengill douche powder in a glass of warm water. I swished it around as best I could. I could scarcely close my lips from the pain of 23 ulcers.
"By the next day I was definitely better and continued to rinse my mouth with douche solution until all the sores were gone. I went back to school on time and have used the remedy ever since."
Other readers have recommended applying powdered alum to the sore, and then rinsing it off. Some people find the tannin in tea helpful, and have found that instant tea powder on a canker sore speeds healing.
Quite a few folks like taking something from the health food store. We've heard from devotees of acidophilus who find the tablets banish canker sores within a day or two.
Other readers prefer prevention. Many people, including dentists, are enthusiastic about the benefits of l-lysine. One person takes 500mg of this amino acid in the morning and another tablet in the evening: "Sometimes I'll get a canker sore but it is gone in two days. I used to get a lot of them and they would be raw at least a week."
A retired dentist suggested discarding all toothpaste containing the foaming agent sodium lauryl sulfate (SLS). He told us about a small but scientific study from Sweden demonstrating that non-SLS toothpaste dramatically reduced canker sores, and recommended Rembrandt Whitening Toothpaste for Canker Sore Sufferers.
While no one has solved the mystery of canker sores, there is no shortage of suggestions on how to get relief.
Write to Joe and Teresa Graedon at Graedon's People's Pharmacy, P.O. Box 52027, Durham, NC 27717-2027. E-mail be sent via their Web site (www.peoplespharmacy.com).