Although the varicose veins that we see are only skin deep, the problem usually lies further underneath the skin. Veins are responsible for getting blood from the legs back up to the heart. Because the blood has to move up against gravity, veins have a series of one-way valves to keep blood flowing up in the right direction. In some people, the veins can become stretched out so that the valve leaflets do not close all the way, and some of the blood leaks backward. This causes the veins below to have increased pressure and therefore start to bulge out. This is what we see from the skin as a varicose vein.