Compression hosiery is the Basic Treatment of venous disease

Because

Compression increases the tissue and oedema pressure in the leg.
Compression reduces the total diameter of the venous vessels in the leg.
Compression maintains a certain level of function of insufficient venous valves.
Compression causes an increase in the body‘s fibrinolytic activity of the venous wall.
Compression supports the effect of the ankle joint and calf muscle pump for the venous blood transport back to the heart.

Compression also acts on the arteries, making advanced arterial obstruction a major contra-indication