MODEL RELEASED. Leg ulcer on the back of the calf of an 85-year-old man. An ulcer is an open sore on the skin, or a mucous membrane, that results in the destruction of the surface tissue. Ulcers are commonly found on the legs and feet, and are often due to an inadequate blood supply. They can also be caused by the infection of a wound. Ulcers need to be kept clean and allowed to heal. Painkilling and anti-inflammatory drugs may also be given during treatment.