A canker sore is a common form of mouth ulcer, which appears as a painful white or yellow ulcer surrounded by a bright red area. A canker sore sore can be triggered by emotional stress, dietary deficiencies, menstrual periods, hormonal changes, food allergies or trauma in the mouth. Canker sores usually heal without treatment within two weeks.
Review Date 4/3/2017
Updated by: Josef Shargorodsky, MD, MPH, Johns Hopkins University School of Medicine, Baltimore, MD. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.