How do varicose veins develop?

In healthy veins, leaflet valves open and close at short intervals in order to guarantee a one-way bloodflow back to the heart, irrespective of gravity forces.

If valves fail to close properly, so-called "reflux" is the result. This means, that blood flows back and forth. Deficient valves are either due to widening of the vein or to degeneration of the leaflets.
Reflux leads to chronic venous hypertension. As a consequence, veins dilate even more, elongate and become tortuous. This is the characteristic appearance of varicose veins.

Blood reflux and venous hypertension cause leakage of blood serum, of proteins and also of blood cells from the veins into the surrounding tissues. This causes tissues to swell up, particularly towards the end of the day. Medium- to long-term consequences are indurations and brownish discolorations of the skin, in particular around the ankles (gaiter area).

In advanced venous disease, the skin can break down thus leading to ulcer formation (lat. ulcus cruris). Consequently, the prominent objective of any treatment for varicose veins is to abolish venous reflux - or, at least, to reduce it.