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What Causes Varicose Veins?

Weak or damaged valves in the veins can cause varicose veins. After your arteries and capillaries deliver oxygen-rich blood to your body, your veins return the blood to your heart. The veins in your legs must work against gravity to do this.

One-way valves inside the veins open to let blood flow through, and then they shut to keep blood from flowing backward. If the valves are weak or damaged, blood can back up and pool in your veins. This causes the veins to swell.

Weak vein walls may cause weak valves. Normally, the walls of the veins are elastic (stretchy). If these walls become weak, they lose their normal elasticity. They become like an overstretched rubber band. This makes the walls of the veins longer and wider, and it causes the flaps of the valves to separate.

When the valve flaps separate, blood can flow backward through the valves. The backflow of blood fills the veins and stretches the walls even more. As a result, the veins get bigger, swell, and often twist as they try to squeeze into their normal space. These are varicose veins.

Normal Vein and Varicose Vein

Figure A shows a normal vein with a working valve and normal blood flow. Figure B shows a varicose vein with a deformed valve, abnormal blood flow, and thin, stretched walls. The middle image shows where varicose veins might appear in a leg.

Figure A shows a normal vein with a working valve and normal blood flow. Figure B shows a varicose vein with a deformed valve, abnormal blood flow, and thin, stretched walls. The middle image shows where varicose veins might appear in a leg.

Older age or a family history of varicose veins may raise your risk for weak vein walls. You also may be at higher risk if you have increased pressure in your veins due to overweight or obesity or pregnancy.

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Varicose Veins Clinical Trials

Clinical trials are research studies that explore whether a medical strategy, treatment, or device is safe and effective for humans. To find clinical trials that are currently underway for Varicose Veins, visit www.clinicaltrials.gov.

 
February 13, 2014 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.