Infected leg ulcer in a 27-year-old man with varicose veins and injuries from playing rugby. An ulcer is an open sore on the skin, or a mucous membrane, that results in the destruction of the surface tissue. Ulcers are often due to an inadequate blood supply. They need to be kept clean and allowed to heal. Varicose veins are veins that have become twisted, distended, and lengthened, due to the presence of defective blood valves. For this ulcer healing after varicose vein surgery, see image C047/8454.