Spider veins are thin vessels, capillaries, connected with the larger venous system. They are small groups of tiny blood vessels located just under the surface of the skin, often resembling a branch or a web in shape. Similar to varicose veins, they are caused by a condition known as venous reflux. Spider veins are the mildest manifestation of venous insufficiency, smaller in size to varicose veins. They can appear isolated or they may be associated with larger, underlying varicose veins. While spider veins can cover large areas of the skin’s surface, they rarely cause physical symptoms.