Sclerotherapy effectively treats spider and varicose veins . It's considered the treatment of choice for small varicose veins. Sclerotherapy involves injecting a solution directly into the vein. The solution causes the vein to scar, forcing blood to reroute through healthier veins. The collapsed vein is reabsorbed into local tissue and eventually fades. After sclerotherapy, treated veins can fade immediately or within a few weeks, although it may take a month or more to see the full results. Depending on veins and desired results several sclerotherapy treatments may be needed.