Spider veins are NOT dangerous and present a cosmetic concern although they can occasionally be associated with some minor aching particularly after prolonged standing. Varicose veins on the other hand can be associated with Deep Vein Thrombosis, Pulmonary Embolism, ulceration of the skin (usually around the ankles), cellulitis (if the damaged skin gets infected) and significant bleeding episodes if the varicose vein is traumatised and bursts. For many people though varicose veins are small and not associated with much in the way of symptoms and the risk of the aforementioned problems is low.