According to The Cleveland Clinic, venous stasis ulcers affect 500,000 to 600,000 people in the United States annually. These ulcers occur when the veins are unable to bring fluid and blood back to the heart. Instead, the fluid pools in the legs, and ulcers develop as a result of the fluid build-up under the skin. Risk factors for developing a stasis ulcer include being overweight, having varicose veins, blood clots in the legs and injury to the legs. You may notice signs and symptoms of venous stasis ulcers on one or both legs.