There are a number of factors that can add to the appearance of varicose veins and spider veins. In a number of cases, the veins are caused by weak valves which create insufficient blood flow. This leads to the appearance of varicose veins.
Varicose veins occur in both men and women. A definitive cause is not known, however a strong family history suggests that some people inherit veins that are more likely to deteriorate. In women, oestrogen may play a role as the onset of puberty, pregnancy and taking oral contraceptives can give rise to vein abnormalities. In pregnancy, the enlarged uterus can restrict blood flow from the legs and promote the development of varicose veins. Spider veins and varicose veins are also associated with obesity. Occupations involving prolonged standing tend to increase the likelihood of veins to develop.