Varicose veins occur when the valves in these superficial veins malfunction. The vein walls can lose elasticity (due to age or hormones), causing them to stretch. When this occurs, the valves may be unable to close, allowing blood that should be moving towards the heart to flow backward (called venous reflux). Blood collects in your lower veins, causing them to enlarge and become varicose. In this manner, faulty valves may cause varicose veins in lower limbs.