Conditions
Canker sore
A canker sore is a painful white or yellow sore that forms inside the mouth, on the cheeks, lips or tongue. It is not the same as a cold sore.
Canker sores, also called aphthous ulcers, are painful white or yellow sores that only form inside the mouth. They usually appear on the insides of the cheeks or lips or on the tongue. They are usually single, round sores with a red border.
Canker sores are not the same as fever blisters, also called cold sores. Fever blisters are small, fluid-filled blisters on the outside of the mouth around the lips. NIDCR lists injury, hormone changes and some body-wide diseases among possible triggers.
NIDCR says tests are rarely needed, but they may be done if sores are severe, do not heal or keep coming back. See also mouth sores and oral thrush.