The most common cause of chronic venous insufficiency (CVI) is incompetent venous valves in the legs. These one-way valves normally prevent blood from flowing backward as it travels up toward the heart, but when they weaken or fail, blood pools in the lower legs and increases pressure inside the veins. This sustained high pressure, called venous hypertension, drives the swelling, skin changes, and ulcers that define CVI. More than 25 million adults in the United States live with some form of the condition.
How Valve Failure Causes the Problem
Your leg veins rely on a system of internal flaps, or valves, that open to let blood move upward and snap shut to prevent it from falling back down. When those valves no longer close properly, blood refluxes, or flows backward, and collects in the veins of the lower leg. The resulting pressure buildup damages the vein walls over time, stretching them further and making additional valves incompetent. This creates a self-reinforcing cycle: more reflux leads to more pressure, which damages more valves.
Valve failure can happen at three levels. In the superficial veins just beneath the skin, valves typically fail because they are weakened, abnormally shaped, or because the vein has widened enough that the valve leaflets can no longer meet in the middle. In the deep veins, valve damage usually results from a prior blood clot (deep vein thrombosis), which inflames the valve, scars it, and narrows the vein channel. A third set of “perforator” veins connects the superficial and deep systems. When perforator valves fail, high pressure from the deep veins transmits directly into the superficial veins, accelerating damage to the skin and tissue underneath.
Primary vs. Secondary CVI
Doctors classify CVI into two broad categories based on what triggered the valve failure. Primary CVI develops gradually, without a specific triggering event. The vein wall weakens over time due to a combination of genetics, aging, and mechanical stress, eventually dilating enough that the valves stop working. This is the more common form.
Secondary CVI follows a specific event, most often a deep vein thrombosis (DVT). After a blood clot forms in a deep leg vein, the inflammatory process scars the valve leaflets and can partially block the vein. This combination of obstruction and reflux is called post-thrombotic syndrome. Prospective studies show that 40 to 50 percent of people who have a first episode of proximal DVT go on to develop post-thrombotic syndrome, and in 8 to 10 percent of those cases the symptoms are severe enough to significantly impair quality of life. In a large international registry, about 28 percent of DVT patients developed post-thrombotic syndrome within three years.
The Role of the Calf Muscle Pump
Valves alone don’t move blood upward. The calf muscles act as a pump: every time you walk or flex your foot, the muscles compress the deep veins and push blood toward the heart. When you sit or stand for long periods without moving, this pump essentially shuts off, and blood stagnates in the lower legs. Over time, a sedentary lifestyle or conditions that weaken the calf muscles (injury, surgery, neurological disease) reduce the pump’s effectiveness and contribute to venous hypertension, even if the valves are still partially functional.
Major Risk Factors
Several factors raise the likelihood of developing CVI, and most of them either increase pressure on leg veins or directly damage valves:
- Age: Vein walls lose elasticity with time. Older adults consistently show higher clinical severity scores.
- Obesity: Higher body mass index correlates with worse clinical presentation. Excess abdominal weight increases pressure in the veins draining the legs.
- Prolonged standing: Occupations that require hours of standing, such as teaching, law enforcement, or bus conducting, keep the calf muscle pump inactive and sustain high venous pressure.
- Pregnancy and multiparity: Hormonal changes relax vein walls, and the growing uterus compresses pelvic veins. Multiple pregnancies compound the effect.
- Family history: Genetics influence vein wall structure and valve formation. A strong family history of varicose veins or CVI raises your risk substantially.
- Prior DVT or leg injury: Any event that scars or obstructs the deep veins sets the stage for secondary CVI.
- Smoking and hormonal therapy: Smoking in men and hormone supplementation in women both increase the risk of DVT, which in turn raises the risk of CVI.
Gender Differences in Severity
CVI is frequently reported as more common in women overall, largely because pregnancy and hormonal factors promote varicose veins and spider veins. The annual incidence of varicose veins is about 2.6 percent in women compared with 1.9 percent in men. But the picture flips when you look at severity. Men consistently present at more advanced clinical stages, with higher rates of skin damage and active ulcers. Women, meanwhile, have higher rates of post-thrombotic syndrome after a DVT. The reasons for these differences are not fully understood, but they suggest that screening matters for both sexes, not just women.
How CVI Progresses
CVI is classified on a seven-point clinical scale (C0 through C6) that tracks visible and measurable changes in the legs:
- C0: No visible signs of vein disease.
- C1: Spider veins or small reticular veins.
- C2: Varicose veins 3 mm or larger in diameter.
- C3: Swelling (edema) in the lower leg.
- C4a: Skin discoloration or eczema around the ankle.
- C4b: Hardening of the skin and underlying fat (lipodermatosclerosis) or white, scarred patches.
- C5: A healed venous ulcer.
- C6: An active, open venous ulcer.
Not everyone progresses through every stage. The three-year risk of developing a first venous ulcer in people already diagnosed with CVI is roughly 4.5 percent, rising to about 5 percent at five years. More than 6 million Americans have advanced-stage disease (C4 through C6), and over 20 percent of those with CVI will eventually develop a venous ulcer at some point.
How CVI Is Detected
The standard diagnostic tool is a duplex ultrasound, which combines a traditional ultrasound image with Doppler flow measurement to visualize blood moving through the veins in real time. A technician compresses and releases segments of the leg while watching for backward flow. If blood flows in the wrong direction for longer than half a second in a superficial vein, or longer than one second in a deep vein, that segment is considered incompetent. The test is painless, takes about 30 to 45 minutes, and is typically performed while you’re standing so gravity can reveal the reflux.
Ultrasound not only confirms whether valve failure is present but also maps which veins are affected, helping guide treatment decisions. Knowing whether the problem is in the superficial system, the deep system, or the perforators changes the approach entirely.
Why Early Attention Matters
Because CVI is progressive, the underlying venous hypertension doesn’t resolve on its own. Compression stockings reduce the pressure in superficial veins and support the calf muscle pump, slowing progression for many people. Weight loss, regular walking, and leg elevation all directly address the mechanical forces that drive the disease. For people with significant superficial reflux, minimally invasive procedures can close or remove the faulty veins, rerouting blood through healthier pathways. Deep vein obstruction from prior clots is harder to treat but can sometimes be managed with stenting.
The earlier valve dysfunction is identified, the more options exist to keep the condition from advancing to skin breakdown and ulceration. People with known risk factors, especially those with a history of DVT, a family history of vein disease, or occupations involving prolonged standing, benefit most from early evaluation.