These enlarged, twisted, and swollen veins usually appear just under the skin of the inner calves or on the backs of the legs, but they can also appear on the thighs. Imagine that the blood in your veins is like a swimming pool. The farther you dive down, the more the pressure increases, says Gabriel Goren, M.D., vascular surgeon and director of the Vein Disorders Center in Encino, California. The pressure in the veins is directly proportional to the height of the person. In other words, in tall people with varicose veins the appearance and symptoms can be more severe than in short people.
Doctors say that genetics and gender play the biggest role.
If you are a woman and one of your parents had varicose veins, then you probably have them, too, especially if you have had multiple pregnancies. Actually, the heart has an ally in the upward-pumping process. Every contraction of your calf muscles helps push blood back toward your heart. In fact, almost 90 percent of all venous blood leaves your legs through the deep veins by the contraction of your muscles. Doctors call it the calf muscle pump or peripheral heart.