Sclerotherapy is a proven medical procedure that has been in use since the 1930s. It is used to eliminate varicose veins and spider veins. During the procedure a solution (generally a salt or an irritating solution) is injected directly into the vein. The solution irritates the lining of the blood vessel, causing it to swell and stick together and the blood to clot. Over time, the vessel turns into scar tissue that fades from view.