Kathy Warwick, age 14, of Phoenix, Ariz., for her question:

WHAT IS A CANKER SORE?

Shallow ulcers that appear under the tongue, on the inside of the lip or elsewhere in the mouth are commonly called canker sores. At first a slight blister appears, and then this rubs off and forms a raw, painful ulcer in the center of a reddened area. The sores may appear singly or in groups.

Sometimes canker sores flare up when a person eats certain types of foods, such as citrus fruits, nuts and chocolate. The name comes from the Latin cancer, which means ulcer.

Relief can be obtained by using ointments that contain antibiotics, but often no treatment will help and the sore will have to run a course of several days to a few weeks before they will disappear. They tend to recur from time to time in certain people.