Description : Canker sore?
Last Answer : DefinitionA canker sore is a painful, open sore in the mouth. Canker sores are white or yellow and surrounded by a bright red area. They are not cancerous.A canker sore is not the same as a fever blister ... School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.