Ulcers can be from pressure on a part of the skin. Ulcers can be from substances that will burn skin or mucous membranes. Peptic ulcers are sometimes from burning by the acid in the stomach. Ulcers can be from cancer. Ulcers can be from diseases of blood vessels. If not enough blood goes to a body part, it can get an ulcer. Stress can also sometimes cause ulcers. Ulcers are often very painful. 