What Is a Canker Sore?

A canker sore is a shallow sore shaped like a crater (ulcer) on your tongue or on the inside of your lip or cheek. Canker sores have a red border and a white or yellow center. They may be painful and can make it hard to talk and eat. You may have one or more than one canker sore at a time. Unlike cold sores, you cannot spread canker sores to other people.

Anyone can get a canker sore, but women, teenagers, and young adults have them more often. People usually get their first canker sore between the ages of 10 and 40. Most people have canker sores at some time in their lives, and some people have them regularly.