Sclerotherapy is a medical procedure that reduces the appearance of varicose and spider veins with the aid of an injection. Sclerotherapy vein treatments take around ten to thirty minutes and can be performed in your doctor's office as an outpatient procedure. How Does Sclerotherapy Work? The patient is injected with a sclerosing agent as pressure is applied to the injected area. While the procedure is relatively painless & doesn't require anesthesia, it is common to experience a mild burning sensation following the injection. The targeted vein swells and either sticks to adjacent veins or scars, forcing blood to reroute through other nearby veins. As the vein heals, scarred veins fade as they are reabsorbed by body tissues.