Varicose veins and spider veins can be caused by weak or damaged valves in the vein. Veins carry blood back to the heart. Usually, when leg muscles contract with activity the blood is pushed back to the heart, working against gravity. Veins have valves that act as flaps, preventing blood from flowing backwards, pooling in the ankles and feet. If the valves get weak, blood can leak back into the lower leg. When backed-up blood makes the veins bigger, they can become varicose. Spider veins can also be caused by hormone changes, exposure to the sun, and injuries.
A number of factors increase the risk of development of varicose and spider veins:
Increasing age is associated with weakening valves in the veins.
Medical and family history, being born with weak valves, and/or having family members with varicose veins increases risk.
Hormonal changes, especially during puberty, pregnancy, and menopause; birth control pills and other medications containing estrogen and progesterone may contribute to the problem.
Pregnancy, when there is 1.5 times the blood volume of the nonpregnant state. The growing uterus puts pressure on the veins. Improvement may occur during the first three months after delivery.
Obesity can put extra pressure on the veins.
Inactivity, such as sitting or standing for long periods of time forces the veins to work harder to pump blood back to the heart.
Sun exposure may cause spider veins on the cheeks or nose of a fair-skinned person.