The main issues are those discussed above under treatment of spider veins. The most important concern is blood clot development in the deep veins of the legs, or deep venous thrombosis (DVT). While we continue to be vigilant in observing safety precautions to prevent DVT, and remain concerned about its potential, we have never had a case of DVT following sclerotherapy. Sometimes segments of the surface veins that were not injected become clotted. There is an associated inflammation with this clotting, and the veins become tender, firm, and often have redness of the skin over them. This is called superficial phlebitis, and is most importantly different from DVT in that these clots do not travel in the bloodstream. Superficial phlebitis, therefore, does not represent a threat, but, because of the tenderness, is a nuisance for a couple of weeks. The other possible untoward effects are discussed more fully under spider vein treatment, but the main concerns are the following. Staining is common following sclerotherapy of varicose veins. This is a light brown discoloration of the skin over the vein. Most of the time, it resolves in a few weeks or months. Occasionally, staining can take 18 months to resolve, and, very rarely, a light brown stain may be permanent, resembling a birth mark. Blushing/matting can occur following varicose vein treatment, and usually indicates the presence of an untreated source of pooling. Skin breakdown is very rare with sclerotherapy for varicose veins. Poor response is unusual, but recurrence is always a possibility.