What Causes Varicose Veins?

Veins, especially those in the legs, have to pump the blood “up hill” to the heart, against gravity. Inside the veins are one-way valves that help with pumping action and prevent blood from flowing backward. These valves allow blood to flow in only one direction, toward the heart. Varicose veins develop when the valves become weakened, damaged, or don’t work well.

Weakness in the valves may be due to weakness in the walls of the veins. This weakness tends to be associated with certain factors, including increasing age, a family history of varicose veins, or high pressure inside veins due to overweight or pregnancy.

When the walls of the veins are weak, they lose their normal elasticity, like an overstretched rubber band. This makes them longer and wider and causes the flaps of the valves to separate. Blood is then able to flow backward through the valves, filling the vein and stretching it even more. The vein becomes enlarged, swollen, and often twisted trying to squeeze into its normal space.

The illustration shows the location of leg veins, which can become varicose veins. Figure A shows a normal vein with working valves and normal blood flow. Figure B shows a varicose vein with deformed valves, abnormal blood flow, and thin, dilated (stretched) walls.