Sclerotherapy, often called spider vein treatment, involves injecting a solution directly in the vein that reduces the appearance of vascular blemishes, spider veins, and broken blood vessels. The sclerotherapy solution causes the vein to scar and collapse, 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 up to a month to see the full results. In some instances, several sclerotherapy treatments may be needed.