a lesion or sore on the skin or mucous membrane resulting from the gradual disintegration of surface epithelial tissue. An ulcer may be superficial, or it may extend into the deeper layer of the skin or other underlying tissue. An ulcer has a depressed floor or crater surrounded by sharply defined edges that are sometimes elevated above the level of the adjoining surface. The main symptom of an ulcer is pain.

The main causes of ulcers are infection, faulty blood circulation, nerve damage, trauma, nutritional disturbances including thiamine or other vitamin deficiencies, and cancer. Such bacterial infections as tuberculosis or syphilis can cause ulcers on any surface of the body. Any infection under the skin, such as a boil or carbuncle, may break through the surface and form an inflammatory ulcer. The ulcers on the legs of persons with varicose veins (varicose vein) are caused by the slow circulation of the blood in the skin. Diabetics (diabetes mellitus) may sustain ulcers on their feet or toes after losing sensation in those areas due to nervous-system damage. A bedsore, or decubitus ulcer, typically occurs on the skin of the back in immobilized or bedridden persons. A peptic ulcer is an ulcer that occurs in the stomach or the first segment of the duodenum, parts of the intestinal tract that are bathed by gastric juice. Ulcers can also result from burns, electric burns, and frostbite.

When an ulcer of the skin has been present for at least one month or is hard to the touch, the possibility of cancer must be considered. The probability of cancer is increased if the patient is past middle age. Ulcers on the border of the lower lip in elderly men are frequently cancers. Such cancers must be recognized and treated early before they spread and become inoperable. By contrast, superficial ulcers on the lips, known as cold sores, are caused by a virus and are not serious. Ulcers in the mouth and throat are frequently caused by infection but are sometimes cancerous, especially in older persons. Cancerous ulcers may also occur in the stomach, small or large intestine, and rectum.