Venous ulcers happen when there’s a break in the skin on your leg, usually around the ankle. The veins in the leg, which should send blood back to the heart, might not be doing their job all that well. That’s often because the valves that stop the flow of blood back into the veins aren’t working like they should. This backflow of blood means increased pressure in the end of the limb. When that happens, it can weaken the skin and make it harder for a cut or scrape to heal.