An ulcer is a crater-like sore on the skin or mucous membrane. Ulcers form when the top layers of skin or tissue have been removed. They can occur in the mouth, stomach, and other parts of the body.
Ulcers can be caused by inflammation, trauma, or infection. Some ulcers may be caused by a cancer.
Reviewed By: Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.