How are canker sores diagnosed?

Canker sores, also called aphthous ulcers or aphthous stomatitis, are diagnosed by their appearance and location. They are small, round, shallow sores in your mouth with a yellow or white center and red edges. They usually form on the insides of your cheeks or lips, on your gums, or under your tongue. Canker sores can be painful but they are rarely serious. Most go away on their own within two weeks.

Your dentist can diagnose a canker sore simply by having you open your mouth and looking at the sore. That's because the symptoms of canker sores are usually marked by small ulcers with a white or gray base and a red border inside the mouth. Canker sores can also be mildly painful and easily irritated. They are not contagious, but can return frequently and may be only one canker sore or several. Canker sores usually heal on their own within a week or two.