Varicose veins or arteries are veins that have become enlarged and tortuous. The term commonly refers to the veins on the leg, although varicose veins can occur elsewhere. Veins have leaflet valves to prevent blood from flowing backwards (retrograde flow or reflux). Leg muscles pump the veins to return blood to the heart (the calf muscle pump mechanism), against the effects of gravity. When veins become varicose, the leaflets of the valves no longer meet properly, and the valves do not work (valvular incompetence). This allows blood to flow backwards and they enlarge even more. Varicose veins are most common in the superficial veins of the legs, which are subject to high pressure when standing. Besides cosmetic problems, varicose veins are often painful, especially when standing or walking. They often itch, and scratching them can cause ulcers. Serious complications are uncommon.