Canker sores are shallow, painful sores in mouth. They are usually red or may sometimes have a white coating over them. One may get them on the inside of your lips, the insides of cheeks or under tongue. Canker sores are different from fever blisters, which usually are on the outside of lips or the corners of mouth.
Anyone can get canker sores, but people in their teens and 20s get them more often. Canker sores may run in families, but they aren’t contagious. Doctors don’t know what causes canker sores, but stress may be a factor.
Unfortunately, doctors don’t know of anything that prevents canker sores from forming. However, using a toothpaste that does not contain SLS (sodium lauryl sulfate) and other irritating ingredients (one brand name: Squigle), avoiding hard or crunchy foods and chewing gum, and getting enough sleep at night may help reduce mouth irritation. If you get canker sores often, or if they’re very painful, talk to your family doctor.