Varicose veins are veins that have become distended and lengthened. They form due to defective valves in the veins of the legs. The valves in the legs usually prevent circulating blood from sinking to the feet under gravity. If the valves stop working, blood can pool downwards, giving the external appearance shown here. The superficial veins (saphenous veins) of the legs are the most commonly affected. Treatment includes wearing elastic support, stripping (the surgical removal of the veins) or sclerotherapy, the injection of a vein with an irritant that eventually blocks it, re-routing the blood.