Some frailty in the inner lining of the vein is considered the reason for the formation of varicose veins. Valves in the vein system are meant to prevent the blood from flowing in the wrong direction i.e. down into the feet. Vein valves are both found in the deep vein system and in the shallow vein system and when they do not operate correctly there is a reflux which causes an increased pressure in the veins below which then dilate and varicose veins are developed. Varicose veins can develop even though there is no reflux in the main veins of the shallow system.
It is probable that the cause for varicose veins may to some degree be attributed to genetic components, i.e. that they are hereditary. However it has been difficult to establish this unequivocally because this is such a common disorder.