Varicose veins, which affect an estimated 10% to 20% of all adults, appear near the surface of the skin as swollen, twisted, blue veins with a "ropy" appearance. Varicose veins develop when the valves in the vein begin to fail, allowing blood to accumulate in the vein. As a result, people who suffer from varicose veins often report that their legs feel heavy and are prone to swelling. Varicose veins may also cause pain or itching. Left untreated, varicose veins are likely to worsen and may result in venous ulceration, a more serious condition.