Sclerotherapy can fail early if the chemical sclerosant is not successful in chemically irritating the endothelial (inside) lining of the veins to cause obliteration. It can also fail late if your body has the ability to heal this inflammatory process and recanalize the veins. No matter which is the case, it can be repeated with great outcomes.
Sclerotherapy is a process. The solution essentially pushes the blood out of the vein and then irritates the vein walls to stick together. Over time the treated veins are absorbed by the body. As time goes on, new veins can occur for many reasons including genetics, sun exposure and aging. Since the treated veins are small, the small clots that occur in the vein are reabsorbed by the body and do not break off and travel elsewhere.