Veins in the legs and elsewhere in the body return used blood back to the heart so it can be oxygenated and recirculated. If a vein is affected by a clot or vascular constriction, blood pressure increases within the vessel and puts pressure on the walls. Eventually, blood begins to leak from the vein and form a stagnant pool in the surrounding tissue. When ulceration occurs near the skin, tissue damage and blood buildup form a dark red lesion.
A leg vein is likeliest to be affected by a varicose ulcer since veins in the lower extremities are relatively far from the heart. While veins in the upper extremities and torso are frequently elevated above the heart, leg veins must fight gravity to return blood. A clot somewhere along a vein or artery in the leg can lead to excess pressure and eventual ulceration. Obesity, high blood pressure, atherosclerosis, and deep vein thrombosis can all contribute to the development of a varicose ulcer