Traditional Chinese medicine(TCM) holds that there are both opposite and unitary relationships between the viscera and tissues, and between the human body and the natural environment. These things maintain a relative dynamic balance through a process in which contradiction alternately appears and disappears, in order to sustain the normal physiological activity of the human body. When this dynamic balance is broken for some reason and can not immediately be restored through self-regulation, certain diseases will occur.

The pathogenic influences breaking up the state of relative balance in the body and leading to diseases are called etiological factors. There are various kinds of etiological factors, such as climatic abnormality, spreading of infectious diseases, improper diet, overstrain, overexertion from bearing weight, external injuries by tripping and falling, wounds by sharp metallic objects, animal or insect bites, etc. Moreover, in the developmental process of disease, the cause and result of disease interact. That is to say, the consequence of disease at one pathological stage may become an etiological factor at another stage. For instance, the phlegm and stagnant fluid, and blood stasis, on the one hand, are the pathologic products of the dysfunction of qi, blood and the viscera. Subsequently, they may become the etiological factors of other diseases.