Dear Dr. Donohue — My 7-year-old daughter has a problem with recurrent canker sores. She's had around six outbreaks a year for the past two years. I'm no expert, but that seems like a lot of canker sores. They're between her gums and lips, top and bottom. What's going on here? — A.A.

Answer — I understand your concern. An outbreak of canker sores every two months is something no child (or adult) should have to endure. The list of conditions that promote recurrent canker sores includes things like iron and B-vitamin deficiencies, possible food allergies, illnesses such as celiac disease and a sensitivity to sodium lauryl sulfate, a common toothpaste ingredient. If your daughter is otherwise healthy and active, the possibility of a link to a serious illness is extremely small. Parents often fear that something must be wrong with the child's immune system. Recurrent outbreaks in one body location rarely are the result of a weak immune system.

It's also worthwhile to look into the food link. This takes more than two or three observations of what she ate in the day or two before an outbreak.

Most canker sores heal in 10 to 14 days. They're not contagious, and probably don't represent an infection. What causes them is an unsettled matter. Recurrences are common, even as many as your daughter has. On the bright side, they tend to lessen as the child grows older.

Diphenhydramine (Benadryl Children's Allergy Liquid), swished in the mouth three times a day and then spit out, can dampen canker sore pain. It doesn't require a prescription. Lidocaine Viscous, which is dabbed on the sore with a cotton-tipped applicator, is another way to deaden the pain.

Dear Dr. Donohue — For many years, I have put up with floaters. I am quite nearsighted, and my eye doctor says they're common in nearsighted people. Last week, I saw flashes of light. I called the doctor, and he saw me that day. He told me I had a vitreous detachment. Is this serious? — L.P.

Answer — The vitreous is a thick, gellike material that fills the back two-thirds of the eye. It provides support for the eye. The vitreous abuts on the retina, the sensitive layer of cells that transfers incoming images to the brain. A vitreous detachment means it has pulled away from the retina. In doing so, it stimulated the retina to cause the flashing lights you saw.

The doctor made sure your retina was OK. Flashes of light also can be a signal that the retina is tearing. For the present, nothing else needs to be done. The doctor will examine you in a few months to be positive the retina is remaining in good health.

Write Dr. Donohue at P.O. Box 536475, Orlando, Fla. 32853-6475.