What are varicose veins and how can you prevent them?

Varicose veins, those bumpy, enlarged blood vessels, usually in the legs, occur when the valves inside the veins fail. The valves are there to keep blood from flowing backward, so when they fail, blood pools lower and lower in the leg, causing the vein to “pop” up toward the surface of the skin. Each time one valve fails, that puts more pressure on the valve below it.