Sclerotherapy is the most common treatment for both spider veins and varicose veins. The doctor uses a needle to inject a liquid chemical into the vein. The chemical causes the vein walls to swell, stick together, and seal shut. This stops the flow of blood, and the vein turns into scar tissue. In a few weeks, the vein should fade. This treatment does not require anesthesia and is done in your doctor’s office. You can return to normal activity right after treatment.