Sclerotherapy or injection of varicose veins is a procedure designed to improve the appearance of your varicose veins. The veins are injected with a solution called a sclerosant which damages the internal lining of the vein and causes blood clotting within the vein. In time, your own body will then destroy the vein and it will disappear. The solution normally used for this procedure is called sodium tetradecyl sulphate (STD) and is available in different concentrations depending on the size of the vein being treated.