Venous insufficiency—often called chronic venous insufficiency (CVI) or venous reflux disease—occurs when leg veins can’t push blood back to the heart efficiently. Faulty one-way valves allow blood to pool in the lower limbs, leading to swelling, aching, skin damage and, in advanced cases, non-healing ulcers. The condition affects up to 40% of adults, yet many people dismiss the early warning signs until complications develop. This evidence-based guide covers everything you need to know: how to spot CVI, why it happens, and the most effective ways to treat and prevent it.