Venous ulcers are caused by incompetent valves in the veins of the lower leg, especially in the perforators. These incompetent valves cause blood to be squeezed out into the superficial veins, when the calf muscles are contracted, instead of upwards towards the heart. Dilation of superficial veins occurs (varicosities) and the subsequent raised venous pressure results in oedema, venous eczema and ulceration. Valves may become damaged following the venous hypertension that occurs in pregnant women, and resulatant varicose veins increase the risk of venous ulcers. Age and immobility are also big risk factors, and women have a longer lifespan than men, so there are more elderly, immobile women.