A canker sore is a painful white ulcer in the mouth. They appear most often on the tongue, inside of the cheeks, and inside of the lips. Unlike cold sores, canker sores are not contagious. But in some people they keep coming back. Canker sores cause pain that may make it difficult to eat or drink.
ByHealthwise StaffPrimary Medical ReviewerKathleen Romito, MD - Family MedicineMartin J. Gabica, MD - Family MedicineAdam Husney, MD - Family MedicineArden G. Christen, DDS, MSD, MA, FACD - Dentistry