Sclerotherapy is a medical procedure used to treat varicose veins and “spider veins.” During sclerotherapy, a solution is injected directly into the affected vein. The solution irritates the lining of the vessel, causing it to swell and stick together. Over time, the vessel turns into scar tissue that fades from view. Sclerotherapy is a well-proven procedure and has been used since the 1930s. Approximately 50-80% of injected veins may be eliminated with each injection session.