Veins have valves that act as one-way flaps to prevent blood from flowing backward as it moves up the legs. Bulging of the veins results when the valves do not function properly, allowing the blood to pool and enlarge the vein. Advanced age can be a major cause of bulging veins. The aging process can cause veins to weaken and lose elasticity, and they become unable to effectively push the blood back toward the heart. As blood pools in the veins, they become enlarged and bulge.
