Varicose veins develop when the one-way valves inside your leg veins stop working properly, allowing blood to flow backward and pool instead of traveling up toward your heart. This pooling increases pressure inside the vein, stretching it outward until it becomes the twisted, bulging cord visible under your skin. The process is gradual, driven by a combination of genetics, lifestyle factors, and the simple challenge of fighting gravity all day long.
How Valves Fail and Veins Stretch
Your leg veins contain small flap-like valves that open to let blood move upward and snap shut to prevent it from sliding back down. When these valves weaken or their leaflets become deformed, thinned, or stuck together, blood reverses direction. This backward flow, called reflux, raises the pressure inside the vein below the damaged valve.
That sustained high pressure does two things. First, it forces the vein wall to stretch outward. The vein itself may already have structural weaknesses: studies of varicose vein tissue show an overproduction of stiff collagen fibers, reduced production of the more flexible type, and a disrupted arrangement of the smooth muscle and elastic fibers that normally give veins their shape and spring. Second, the high pressure triggers inflammation. White blood cells accumulate around the stressed valve, and the enzymes they release gradually remodel and thin the valve leaflets further. The damage feeds on itself: weakened valves create more pressure, and more pressure weakens more valves.
The veins closest to the skin surface are especially vulnerable because they lack the structural support that muscles provide to deeper veins. When pressure from the deep system transmits backward through connecting veins into the superficial system, those thinner-walled surface veins are the ones that balloon outward and become visible.
The Role of Your Calf Muscles
Your calf muscles act as a built-in pump for venous blood. Every time you take a step, your calf contracts and squeezes the deep veins inside the muscle, pushing blood upward. During the relaxation phase, blood is drawn from your surface veins into the deeper ones through short connecting veins called perforators. This rhythmic pumping keeps pressure in your surface veins low while you’re moving.
When this pump fails or simply doesn’t activate often enough, the whole system backs up. Standing or sitting still for long stretches means your calves aren’t contracting, so blood sits in your lower legs under the full weight of the column of fluid above it. Over time, that sustained pressure stretches veins and stresses valves. Walking and running both increase the pump’s output in proportion to how fast you’re moving, which is one reason regular movement is so protective. Even simple calf raises activate the same mechanism.
Why Some People Are More Prone
Genetics play a significant role. In one study, more than half of women with varicose veins had a parent with the condition. The structural qualities of your vein walls, the strength of your valves, and the amount of connective tissue supporting your veins are all inherited traits. If both your parents have varicose veins, your risk is substantially higher than someone with no family history.
Beyond genetics, several factors raise your odds:
- Age. Vein walls lose elasticity over time, and valve leaflets wear down after decades of opening and closing thousands of times a day.
- Pregnancy. Blood volume increases significantly during pregnancy, putting extra pressure on leg veins. Hormonal changes also relax vein walls. Varicose veins that appear during pregnancy sometimes improve within a few months of delivery, but they often worsen with each subsequent pregnancy.
- Prolonged standing or sitting. Jobs that keep you on your feet or at a desk for hours reduce calf pump activity, letting pressure build in your lower legs.
- Excess weight. Additional body weight increases the pressure your leg veins have to push against, accelerating valve damage.
- Sex. Women develop varicose veins more often than men, likely due to hormonal influences on vein wall elasticity, particularly during pregnancy and menopause.
What Happens If They Get Worse
For many people, varicose veins are a cosmetic concern and a source of aching or heaviness after long days. But they exist on a spectrum of venous disease that can progress. Early on, you might notice swelling around your ankles by the end of the day. Over months or years, chronic high pressure in the veins can cause skin changes around the lower leg: darkening, thickening, or a leathery texture. In more advanced cases, the skin can break down into slow-healing ulcers near the ankle.
Blood that pools in varicose veins can also clot, causing a condition called superficial thrombophlebitis. The vein feels hard and tender, and the skin over it may turn red. This is painful but usually not dangerous on its own. Deep vein clots are a separate and more serious concern, though varicose veins themselves are a relatively modest risk factor for those.
How Varicose Veins Are Diagnosed
A doctor can often identify varicose veins just by looking at your legs while you’re standing. To understand the extent of the problem and plan treatment, they’ll typically order a duplex ultrasound. This painless scan shows both the structure of your veins and the direction of blood flow in real time. Blood that flows backward for more than half a second after the calf is squeezed and released is considered abnormal reflux. That half-second threshold is the standard cutoff used to distinguish normal valve closure from a valve that’s failing.
Treatment Options and What to Expect
Conservative management works well for mild symptoms. Compression stockings squeeze the surface veins and help push blood upward, reducing pooling and swelling. Regular walking, elevating your legs when resting, and maintaining a healthy weight all support your calf pump and lower venous pressure.
When varicose veins cause persistent symptoms or skin changes, procedures can close or remove the damaged vein. The most common approach today is endovenous thermal ablation, where a thin catheter is inserted into the vein and uses heat to seal it shut from the inside. It’s done under local anesthesia, typically takes under an hour, and most people return to normal activity within a day or two. After one year, thermal ablation successfully closes the treated vein about 88% of the time.
Foam sclerotherapy is another option, especially for smaller veins. A foam solution is injected into the vein, irritating its walls until they stick together. It’s less invasive and requires no anesthesia, but its one-year success rate is lower, around 72%. Traditional surgical stripping, which physically removes the vein through small incisions, has similar long-term results to thermal ablation but involves more recovery time.
Closing or removing a varicose vein doesn’t hurt your circulation. The blood simply reroutes through healthier veins. However, new varicose veins can develop over time in other locations, especially if the underlying risk factors like genetics, weight, or prolonged standing remain in play.