Varicose veins develop when the one-way valves inside your leg veins stop working properly, allowing blood to flow backward and pool instead of returning to your heart. This backward flow, called reflux, stretches the vein walls over time until they bulge visibly beneath the skin. The process is rarely sudden. It results from a combination of genetics, lifestyle, hormonal shifts, and the simple wear of gravity on your body over years.
How Valves Fail Inside Your Veins
Your leg veins contain a series of tiny flap-like valves that open to let blood move upward toward your heart and snap shut to prevent it from sliding back down. These valves work together with your calf muscles, which act like a pump every time you walk or flex your legs. When your calf muscles contract, they squeeze blood upward through the deep veins. The valves then close behind it, holding the progress in place against gravity.
When standing still, the blood column between your heart and feet creates significant pressure at your ankles, roughly 115 mm Hg. Walking normally reduces that pressure by 60% to 80%, thanks to the calf muscle pump. But if the valves weaken or the pump stops working efficiently (from prolonged sitting or standing, for example), that pressure stays high. The sustained force stretches the vein walls, which in turn pulls the valve flaps apart so they can no longer seal properly. Once one valve fails, the added pressure cascades downward, overloading the next valve below it.
This process can start in the deep veins, the superficial veins closer to the skin surface, or the short connecting veins (perforators) between the two systems. When perforator valves fail, high-pressure blood from the deep system gets forced backward into the superficial veins with enough power to dilate them and destroy their valves too. That’s why varicose veins tend to worsen over time rather than stabilize.
Genetics Is the Strongest Risk Factor
Family history plays a larger role than any single lifestyle factor. A Swedish adoption study separated genetic influence from shared household habits by comparing adoptees with affected biological parents to those with affected adoptive parents. Adoptees who had a biological parent with varicose veins were 2.2 times more likely to develop them, even when raised in a different household. Adoptees whose adoptive parent had varicose veins but whose biological parents did not showed no increased risk at all.
When both a biological parent and an adoptive parent were affected, the risk jumped to 4.6 times higher, suggesting that genetic vulnerability combined with a shared environment (similar activity levels, diet, or posture habits) compounds the effect. The inherited component likely involves the structural proteins in vein walls. People predisposed to varicose veins tend to have vein tissue where the elastic fibers fragment and lose their organized layered structure, while collagen accumulates in abnormal patterns that stiffen the wall without strengthening it.
How Hormones Weaken Vein Walls
Estrogen and progesterone both directly affect vein structure, which is a major reason varicose veins are more common in women. Estrogen normally helps maintain the tone and elasticity of blood vessels, but at elevated levels it causes vein walls to relax and dilate. Progesterone compounds this by relaxing the smooth muscle cells within the vein walls, reducing their ability to push blood upward. The combined effect is looser, more distensible veins that pool blood more easily.
These hormonal shifts hit hardest during pregnancy and around menopause. During pregnancy, estrogen and progesterone surge simultaneously, weakening both the vein walls and the valve leaflets. After menopause, falling estrogen levels reduce collagen production, degrading the structural scaffolding that keeps veins firm. Hormonal contraceptives and hormone replacement therapy can also contribute by keeping estrogen or progesterone levels artificially elevated for long periods.
Why Pregnancy Is a Perfect Storm
Pregnancy combines nearly every risk factor for varicose veins at once. Blood volume increases by roughly 45% above pre-pregnancy levels (and can rise as high as 100% in some women), flooding the venous system with far more fluid than it normally handles. The growing uterus compresses the large veins in the pelvis, partially blocking the return path from the legs to the heart. Meanwhile, the hormonal changes described above are loosening vein walls and softening valve tissue.
The result is that many women develop their first visible varicose veins during pregnancy, particularly the second or third trimester. Veins often improve somewhat after delivery as blood volume drops and hormonal levels normalize, but the structural damage to valves may not fully reverse. Each subsequent pregnancy tends to make existing varicose veins worse, because the valves start from a weaker baseline.
Weight, Standing, and Inactivity
Carrying extra body weight puts sustained additional pressure on the veins in your legs. Research comparing over 1,400 patients found a clear, stepwise relationship between body mass index and venous disease severity. Overweight patients (BMI 25 to 29.9) had significantly more valve failure and higher clinical severity scores than normal-weight patients. Obese patients (BMI 30 and above) had even more extensive reflux, including damage to the deep venous system. Importantly, this relationship held regardless of how long someone had been living with venous disease, suggesting that excess weight is an independent accelerator rather than just a consequence of having the condition longer.
Prolonged standing or sitting starves the calf muscle pump of work. Without regular contraction cycles, blood sits in the lower leg veins under full gravitational pressure. Jobs that involve standing in one position for hours (retail, factory work, teaching, surgery) are consistently associated with higher rates of varicose veins. Sitting for long stretches is similarly problematic because the calf muscles are inactive and the veins in the back of the thigh are partially compressed, slowing return flow. The fix isn’t vigorous exercise so much as regular movement: walking, shifting weight, flexing your calves, or simply changing position throughout the day.
What Aging Does to Your Veins
Time works against vein health in two ways. First, the structural proteins in vein walls degrade. Elastic fibers, which allow veins to stretch and snap back, fragment into scattered clumps. Collagen fibers, which provide strength, accumulate in disorganized patterns that thicken the wall but reduce its flexibility. The vein becomes simultaneously stiffer and weaker, less able to maintain its shape under pressure. Second, the number of functional cells in the vein wall decreases, reducing the tissue’s ability to repair itself or adapt to stress.
These changes are nearly universal with aging and overlap significantly with the tissue changes seen in varicose veins themselves. By the time most people reach their 50s and 60s, the cumulative effect of decades of gravitational pressure on progressively weakening tissue makes some degree of venous insufficiency extremely common.
How Varicose Veins Progress
Venous disease follows a recognized progression. The earliest visible signs are spider veins: tiny red or purple clusters near the skin surface. These are largely cosmetic. True varicose veins are the next stage, appearing as raised, twisted, bluish-green cords typically on the calves or inner thighs. At this point, you may notice aching, heaviness, or throbbing in your legs, especially after long periods of standing.
If the underlying pressure goes unmanaged, the disease can advance further. Swelling around the ankles that persists through the day signals worsening fluid backup. Over time, chronic high pressure in the small vessels near the skin can cause brownish discoloration around the ankles, itchy rashes, and hardening of the skin and underlying fat. The most advanced stage is the development of venous ulcers, open wounds near the ankle that heal slowly and tend to recur. Not everyone progresses through all these stages. Many people live with stable varicose veins for decades without significant complications, particularly if they manage the modifiable risk factors.
Factors You Can and Cannot Control
You cannot change your genetics, your age, or (in most cases) whether you become pregnant. These are the dominant drivers. What you can influence is how much additional stress your veins endure:
- Movement throughout the day. Even brief walks or calf raises activate the muscle pump and drop venous pressure in your legs substantially.
- Body weight. Reducing BMI from the obese to the normal range meaningfully lowers the severity of venous disease and improves outcomes if treatment becomes necessary.
- Leg elevation. Raising your legs above heart level for periods during the day lets gravity assist rather than oppose venous return.
- Compression stockings. Graduated compression from the ankle upward mimics the effect of muscle contraction, keeping blood moving and reducing pooling.
- Avoiding prolonged static postures. If your job requires standing or sitting for hours, scheduled movement breaks are the single most practical intervention.
None of these measures can fully prevent varicose veins in someone with strong genetic predisposition, but they can slow progression and reduce symptoms considerably. The underlying biology is a mismatch between the pressure gravity places on leg veins and the structural capacity of those veins to handle it. Anything that tips the balance, whether genetics, hormones, weight, or inactivity, moves you closer to visible disease.