Most women with spider veins have mothers and/or female relatives with this vein condition. Weak vein walls and valves, as well as shortage of vein valves, seem to be inherited characteristics, and may play a role in determining who develops spider veins and at what age.
Pregnancy
During pregnancy, and to a lesser degree also during periods, fluctuations in the female sex hormone (especially estrogen and progesterone), cause softening of the vein walls and valves. This makes women's veins more prone to stretching and enlargement with increased pressure. Increased blood volume, which is needed to provide circulation to the fetus, also cause increased pressure on the vein walls. The growing fetus also exerts pressure on the pelvis, which in turn, exerts pressure on the leg veins. Some women see spider veins that develop during their pregnancies and persist after their baby is born. Other see that their veins disappear after the baby is born, only to reappear later in life.
Prolonged standing and sitting
Prolonged standing and sitting cause a great amount of pressure to develop in the leg veins. In both conditions, the calf muscles are inactive and therefore cannot help push the venous blood to return to the heart. This causes blood to pool in the veins, thus resulting in increased pressure on the vein walls.
This pressure drops once one begins to walk, so if your job requires you to stand or sit for prolonged periods, remember to take short breaks and walk around for a couple of minutes every hour.
Injury
In some people, spider veins appear after injury or trauma to the vein, such as after a broken ankle, surgery, car accident, or sports injury. Bruising, which is pooled blood resulting from broken veins under the skin, can also lead to an inflammatory response, which in turn, can result in enlarged veins. Sometimes, spider veins can appear many years after the wound has healed.
Vein Conditions
In men, spider veins are usually the result of blow-outs from nearby varicose veins. High pressure from these veins cause adjoining superficial veins to stretch, enlarge, and change in color. These spider veins are usually darker and have larger diameters than the spider veins in women. Spider vein matting, which resemble bruises that do not go away, is often caused by the healing process of injuries and bruises, as well as complications from sclerotherapy. Ankle flares, or spider veins found on the inside ankle, is often associated with chronic venous insufficiency (CVI), a condition where venous blood is not returned efficiently to the heart.
