In healthy veins leaflet valves, that open and close, allow blood to flow back to the heart against gravity forces. (So these valves prevent blood from flowing backwards).
If these valves fail to close properly, a damaging backflow (reflux) occurs which leads to a backlog of blood in the veins of the leg. The veins widen, elongate and dilate and take a wriggled shape to form the characteristic shape of a varicose vein.
Over the time the permanent pressure of the blood reflux leads to an increased outlfow of liquid, protein and blood cells into the surrounding tissue.This causes the skin to swell, harden and turn brownish, in particular in the region above the ankle joints.
In severe cases skin and fat tissue is so much under-supplied with blood that this leads to an „open leg“ (lat. ulcus cruris). Therefore the ultimate objective of any therapy is to avoid the malicious venous reflux of the blood.