What causes varicose veins? Understanding the underlying factors

Most people recognise varicose veins by their bulging, rope-like appearance—but few know why they form. In simple terms, varicose veins develop when blood flow in the legs is disrupted and pressure builds up in the veins. But the causes of that pressure are often more complex.

In this article, we’ll explain how varicose veins develop, what puts you at higher risk, and what you can do to reduce your chances of developing them.

How do varicose veins form?

Your veins contain small valves that help blood flow in the right direction—back up to the heart. When those valves become weak or damaged, blood begins to flow backwards and pools in the veins. Over time, this increases pressure inside the veins, causing them to stretch, twist, and become visibly enlarged.

This process is known as chronic venous insufficiency, and it’s the underlying condition behind most cases of varicose veins.

You can learn more about this mechanism in our article on venous insufficiency: symptoms, causes, and treatments.

Why do varicose veins appear in the legs?

The veins in your legs have to work against gravity to return blood to the heart. When you sit or stand for long periods, this challenge becomes even greater—and that’s why the lower legs are the most common site for varicose veins.

Your leg veins are also longer and more vulnerable to pressure changes than other veins. If your valves are even slightly weakened, this is where symptoms are most likely to start.

Read more in our article on early-stage varicose veins symptoms.

Key causes and risk factors

Varicose veins don’t happen for just one reason. Several factors tend to work together to increase your risk:

• Genetics: If one or both of your parents had varicose veins, your own risk is significantly higher.
• Hormonal changes: Pregnancy, menopause and hormonal medications can weaken vein walls and valves.
• Age: As you age, your vein walls and valves become less elastic and more prone to damage.
• Gender: Women are more likely to develop varicose veins, likely due to hormones and pregnancy-related changes.
• Occupation: Jobs that involve long periods of standing or sitting (e.g. teachers, nurses, office workers) put extra pressure on your leg veins.
• Weight: Extra weight increases pressure in your legs and can strain your vein system.
• Lack of movement: Prolonged sitting or standing slows circulation and makes it harder for your veins to push blood upwards.

Discover helpful strategies in our guide on how to avoid varicose veins.

Are all varicose veins visible?

No—some people have hidden varicose veins (also called internal varicose veins), where the affected veins lie deeper under the skin. These may not be immediately visible but can still cause symptoms like:

• aching or heavy legs
• night cramps
• swelling around the ankles
• itching or burning sensation

If these signs sound familiar, explore our article on hidden varicose veins symptoms for more guidance.

When should you seek medical advice?

If you have persistent leg discomfort, visible veins, swelling, or skin changes, it’s worth getting your veins assessed. A quick ultrasound can determine if your valves are working correctly or if treatment for varicose veins is needed.

Learn more about what’s involved in a consultation at UK Vein Care.

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