Close-up of leg ulcers on the leg of an eighty seven year old woman with chronic venous insufficiency. Chronic venous insufficiency occurs when blood doesn't flow back to up to the heart, causing it to pool in the legs. 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. Ulcers need to be kept clean and allowed to heal. Painkillers and anti-inflammatory drugs may also be given during treatment.