Venous ulcers (open sores) can occur when the veins in your legs do not push blood back up to your heart as well as they should. Blood backs up in the veins, building up pressure. If not treated, increased pressure and excess fluid in the affected area can cause an open sore to form.
Most venous ulcers occur on the leg, above the ankle. This type of wound can be slow to heal.
The veins in your legs have one-way valves that keep blood flowing up toward your heart. When these valves become weak, blood can flow backward and pool in your legs. This is called venous insufficiency. The excess fluid causes the blood pressure to build up in your legs. The increase in pressure and buildup of fluid prevents nutrients and oxygen from getting to tissues. The lack of nutrients causes cells to die, damaging the tissue, and a wound can form.