Sclerotherapy effectively treats spider veins. It’s often considered the treatment of choice for small varicose veins. Sclerotherapy involves injecting asclera directly into the vein. The asclera 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 tend to fade within a few weeks, although occasionally it may take a month or more to see the full results. In some instances, several sclerotherapy treatments may be needed to achieve desired results.