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: Kevin Berman, MD, PhD, Atlanta Center for Dermatologic Disease, Atlanta, GA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.