Varicose veins can develop through a combination of weakened vein walls and faulty valves. Varicose veins are enlarged, twisted rope-like veins appearing near the surface of the skin. While they can develop anywhere in the body, they are most commonly found in the legs and ankles because standing and walking increase pressure in the lower extremities. Under a variety of circumstances, normally toned, elastic vein walls can become weak and allow the recirculating blood that should be moving toward your heart to flow backward. One-way valves in these veins – which open and enable blood to flow through on its way upward, then close to stop blood from flowing backward – can also fail to function properly. This allows blood to pool and pressure to build up, which further weakens and subsequently damages the veins, causing them to become twisted, enlarged and painful. This venous reflux, or venous insufficiency, leads to the development of varicose and spider veins. Up to 40% of women and 25% of men are affected by this condition – but fortunately, treatment is available.