What are canker sores?
Canker sores are shallow, painful sores in the mouth. They are usually red or may sometimes have a white coating over them. You might get them on the inside of your lips, the insides of your cheeks, the base of your gums or under your tongue. Canker sores are different from fever blisters, which usually are on the outside of your lips or the corners of your mouth. Canker sores are also called aphthous ulcers.
Anyone can get canker sores, but women and 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 exactly what causes canker sores. Mouth injuries, stress, poor nutrition, food allergies and menstrual periods are some of the things that may increase your chances of getting a canker sore.
Written by familydoctor.org editorial staff