The circulation of the blood is a perfect system: the heart pushes blood through the arteries – as far as the toes. The leg muscles (calf muscle pumps) compress it in the veins and return it back to the heart against gravity. The valves in the veins ensure that it doesn't flow downwards again and pool in the leg veins. If the valves aren't working, the blood stagnates in the veins and varicose veins occur. The increased pressure in the varicose veins caused by the congestion makes the fluid and other constituents of blood escape from the vessels into the tissue. In turn, this impairs the supply of oxygen and nutrients to the affected areas of tissue. The skin becomes discoloured, feet and legs swell up. A minor injury is sufficient to cause an ulcer to develop, which is hard to heal. This is a venous leg ulcer.

The statutory health insurance schemes in Germany pay out more than one billion Euro a year for the treatment of venous leg ulcers.

The open wound is very painful. Germs that settle and colonise the wound and its surroundings cause unpleasant odours. For this reason those affected often don't dare mix with other people. The pain causes them to keep their leg still and hardly move it at all. In turn this means that the pump mechanism which moves the blood in the direction of the heart is switched off. A vicious circle begins.