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Varicose Veins

Why Do Varicose Veins Occur?

Thursday, June 14, 2012 - 13:11

Varicose veins causes are myriad. Although experts do not know exactly what causes varicose veins, most agree that varicose veins occur because of problems with the valves in the veins.

Valves consist of two thin flaps of tissue (hence they are called bicuspid valves) that open in one direction to allow deoxygenated blood to flow back to the heart. In normal, healthy valves, the two flaps of tissue close tightly, preventing blood from flowing backwards. If valves are damaged, they may not be able to close completely, and blood may leak downward and collect in the vein (called venous insufficiency). 

For more about how valves in veins function, see What are Varicose Veins?

Valves may fail for several reasons:

  • There may be an inadequate number of valves, or the valve may be defective.
  • The vein walls may be weak. Veins with weak walls bulge and damage the valves by pulling the delicate leaves of the valves apart.
  • Valves may be damaged by blood clots. Although the clot dissolves, valves may become scarred. These damaged valves then fail to operate properly.
  • In some cases, the vein itself may be at fault. Obesity, pregnancy, or periods of prolonged standing may put excessive pressure on a leg vein, causing the walls of the vein to bulge. When this happens, the two halves of the valve are forced too far apart, and they cannot completely block blood from flowing backwards during the closing phase. Thus, some blood is allowed to flow downward.
  • Anything that causes strain for a lengthy time may lead to increased pressure on leg veins and weakened valves. Conditions that may cause problems with valves include chronic cough or constipation and urinary retention due to an enlarged prostate.
  • Aging may coincide with valve problems. Almost all people older than 65 have some varicosities.


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