Sclerotherapy is a well-known treatment for spider veins and varicose veins. It has a proven track record for success and is known to be a relatively painless vein procedure. One of the reasons that foam sclerotherapy may be a preferred method of treatment is that it does not require an anesthetic. Even with the "foam" aspect, treatment is performed using a tiny needle. Another reason that a doctor may prefer foam sclerotherapy is that the thicker consistency of the sclerosing agent may be more efficient at sticking to the walls of larger veins that need to be collapsed.