Vein valves malfunction due to several reasons. The most common cause is hereditary weak valves. The microscopic make-up of the valves is abnormal in people who have parents with vein problems. These weak valves give way, causing venous insufficiency.

Female hormones, especially progesterone, cause the valve tissue to soften and give way. Progesterone also causes the vein walls to dilate, which pulls the valves apart and causes them to leak blood backward.

Pregnancy puts additional stress on vein valves, primarily due to a 100x increase in blood progesterone levels, which causes the veins and valves to dilate. Increased blood volumes also cause the veins and valve to stretch and fail.

Blood clots can form on valves and cause them to scar and be stuck in the open position, allowing blood to reflux in the wrong direction.

Lastly, age, gravity and prolonged standing and sitting can wear the valves out, just like other body parts. The weakened valves give out and allow gravity to cause blood to pool in the legs.

For more information see Frequently Asked Questions about Vein Conditions.