Varicose veins are enlarged, swollen, and twisting veins, often appearing blue or dark purple. They happen when faulty valves in the veins allow blood to flow in the wrong direction or to pool. They almost always affect legs and feet. Visible swollen and twisted veins -- sometimes surrounded by patches of flooded capillaries known as spider veins -- are considered superficial varicose veins. Although they can be painful and disfiguring, they are usually harmless. When inflamed, they become tender to the touch and can hinder circulation to the point of causing swollen ankles, itchy skin, and aching in the affected limb. Besides a surface network of veins, your legs have an interior, or deep, venous network. On rare occasions, an interior leg vein becomes varicose. Such deep varicose veins are usually not visible, but they can cause swelling or aching throughout the leg and may be sites where blood clots can form. Varicose veins are a relatively common condition, and for many people they are a family trait.