Varicose veins develop when small one-way valves inside your leg veins stop working properly, allowing blood to flow backward and pool instead of returning to your heart. About 23% of U.S. adults have them, and the causes range from genetics and hormones to the simple demands of daily life. Understanding what’s actually happening inside the vein helps make sense of who gets them and why.
How Valves Fail and Blood Pools
Your leg veins have a tough job. They push blood upward against gravity, back toward your heart, using a series of tiny valves that open to let blood through and snap shut to prevent it from sliding back down. When one of these valves becomes damaged or weakened, it can’t close completely. Gravity takes over, and blood flows backward, a situation called venous reflux.
That backward-flowing blood collects in the vein, increasing pressure on the walls. Over time, the vein stretches, bulges, and becomes the twisted, rope-like line visible under the skin. This isn’t just a surface problem. Research on varicose vein tissue shows that the elastic fibers in the vein wall break down significantly in the dilated sections, while the collagen (the stiffer structural protein) stays roughly the same. The result is a vein that has lost its ability to snap back into shape, like a rubber band that’s been stretched too many times. That shift in the vein wall’s composition helps explain why varicose veins tend to get worse rather than better on their own.
Genetics Play a Major Role
Family history is the single strongest predictor. A study of 134 families published in the AHA’s Circulation: Cardiovascular Genetics found that when both parents had varicose veins, their children faced a 90% chance of developing them too. Even having one affected parent raises your risk substantially. The inherited component likely involves the structure of the vein wall itself and how well the valves are built, which means some people are predisposed long before any lifestyle factor comes into play.
Why Women Are Affected More Often
Varicose veins affect roughly twice as many women as men. Between ages 40 and 80, an estimated 22 million American women have them compared to 11 million men. Hormones are a big part of the reason.
Progesterone, which rises sharply during pregnancy and fluctuates throughout the menstrual cycle, relaxes the smooth muscle in vein walls. That relaxation makes the valves less effective at sealing shut. During pregnancy, this effect is compounded by a dramatic increase in blood volume (your body produces roughly 50% more blood to support the fetus) and by the growing uterus pressing on the large veins in the pelvis, which slows return flow from the legs. Many women notice varicose veins for the first time during pregnancy, and while some improve after delivery, the vein changes often persist or worsen with each subsequent pregnancy.
Hormonal birth control and hormone replacement therapy can have similar, though milder, effects on vein wall elasticity.
Standing and Sitting for Long Hours
Your calf muscles act as a pump, squeezing veins with every step to push blood upward. When you stand or sit still for hours, that pump barely activates, and blood sits in your lower leg veins under sustained pressure. Research published in the Scandinavian Journal of Work, Environment & Health found that women who work mostly on their feet have 2.6 times the risk of varicose veins compared to women in other positions. For men, the risk was 1.85 times higher.
Jobs most associated with this include nursing, teaching, retail, factory work, and food service. Prolonged sitting, especially with legs crossed or bent at the knee, creates a similar problem by compressing veins and reducing circulation. The common thread is any position that keeps your calf muscles inactive for extended periods.
Age, Weight, and Other Contributors
Age is an unavoidable factor. Vein valves wear out over decades of constant use, and the elastic tissue in vein walls naturally degrades. Varicose veins are uncommon before age 30 and increasingly prevalent after 50.
Carrying extra weight adds sustained pressure to leg veins, especially in the abdomen and pelvis, which restricts blood flow returning from the legs. This is similar to the mechanical effect of pregnancy but chronic rather than temporary. A history of blood clots in the deep leg veins can also damage valves permanently, leaving them unable to close. Previous leg injuries or surgeries that affect vein structure raise the risk for the same reason.
What Happens If They Go Untreated
Many varicose veins are a cosmetic concern that causes aching, heaviness, or itching but nothing more. In some cases, though, the underlying venous pressure leads to real complications over time. Chronic pooling of blood increases fluid buildup in surrounding tissue, which can eventually cause venous ulcers, slow-healing open wounds near the ankle that are painful and prone to infection. The skin around the affected veins may harden, change color, and swell, a condition called lipodermatosclerosis. Stagnant blood flow in varicose veins also raises the risk of blood clots forming in the deeper veins, known as deep vein thrombosis, which can become dangerous if a clot travels to the lungs.
These complications don’t happen to everyone, but they’re more likely when varicose veins are large, symptomatic, or have been present for years.
Reducing Your Risk
You can’t change your genetics or stop aging, but several practical steps reduce the pressure on your leg veins. Moving your legs frequently throughout the day is the most effective strategy. If your job requires standing, shifting your weight, rising onto your toes, and taking short walking breaks keeps the calf muscle pump active. If you sit for long stretches, flexing your ankles and getting up every 30 to 60 minutes makes a meaningful difference.
Compression stockings apply graduated pressure to the legs, tightest at the ankle and loosening as they go up, to help push blood back toward the heart. For prevention and mild symptoms, moderate-pressure stockings in the 15 to 20 mmHg range are typically sufficient. If you already have noticeable varicose veins or moderate swelling, firm compression at 20 to 30 mmHg is more appropriate. Elevating your legs above heart level for 15 to 20 minutes at the end of the day also helps drain pooled blood.
Regular exercise, particularly walking, cycling, or swimming, strengthens the calf muscles and improves overall circulation. Maintaining a healthy weight removes one of the persistent mechanical forces that contribute to vein damage over the long term.