When the body is in balance between Yin and Yang health is predominant. When the Yin and Yang are imbalanced, disease occurs.

The original meaning of Yin-Yang was the bright side- dark side. Yang is the bright side and Yin is the dark side. Everything in the world can be described, explained and further divided into the Yin-Yang phenomena. The basic properties of heat, brightness, activeness, outwardness, upwardness, hyper function belong to Yang. The basic properties of coldness, darkness, stillness, inwardness, downwardness, hypo function belong to Yin. Yin and Yang oppose each other and at the same time have an interdependent relationship. Without Yang there is no Yin, without Yin there is no Yang.

Application of Yin and Yang theory to anatomy & physiology

Physically speaking: The upper part of the body, The exterior part of the body, and the back are all Yang. The lower part of the body, the interior part of the body, and the abdomen are all Yin. The five zang are Yin, the six fu organs are Yang. Within each organ, there is Yin and Yang aspects, such as heart-Yang, heart-Yin, kidney-Yang and kidney-Yin.

Physiologically speaking: Yin can be viewed as the substance aspect and Yang can be viewed as the functional aspect.

Pathology according to Yin-Yang theory Yin pathogens and yang pathogens. Diseases caused by Yang pathogens usually present with heat symptoms, and diseases caused by Yin pathogens usually present with cold symptoms. Except for deficient-Yin which presents with heat symptoms. And deficient-Yang which present with cold symptoms.