Varicose veins are large, swollen, twisted veins, dark blue or purple in color, that often appear on the legs and feet. They occur when the valves in the veins do not work properly, so the blood does not flow effectively. In some cases it is only an aesthetic concern. However, many people experience painful symptoms such as swelling, throbbing, burning, itching, cramping, or a heavy, achy feeling in the legs or feet. In some cases, patients experiencing these symptoms may not have any visible varicose veins. The diseased veins can occur deep under the skin, invisible to the naked eye.