The root of the problem is increased pressure of blood in the veins of the lower leg. This causes fluid to ooze out of the veins beneath the skin. This causes swelling, thickening and damage to the skin. The damaged skin may eventually break down to form an ulcer.
The increased pressure of blood in the leg veins is due to blood collecting in the smaller veins next to the skin. The blood tends to collect and pool because the valves in the larger veins become damaged by a previous blood clot (thrombosis) in the vein or varicose veins. Gravity causes blood to flow back through the damaged valves and pool in the lower veins. Some of the main causes of venous skin ulcers include:
