Foundations of TCM
Pathogenic Factors (Liu Yin)
Pathogenic Factors (Liu Yin), sometimes also referred to as the six excesses, are climatic influences that invade the body though the exterior and cause disease. They include Cold, Heat, Summer-Heat, Dampness, Dryness and Wind. The invasion of a Pathogenic Factor always represents an Excess-pattern and must be treated accordingly (sedative, i.e. dispelling). The Pathogenic Factors invade the body via the skin and can stay in different levels. The first level is the superficial level, which involves the skin and the tendino-muscle Channels. The next level involves the Channels, and the last levels involve the Zang Fu organs. Different theories about the invasion of pathogenic factors have been composed over time. In the Classics, namely the Wen Bing Lun, four levels, progressing in depth of invasion, are described: Wei, Qi, Ying (nutritive) and Xue (Blood) level. This theory was formed to complement the much earlier theory of the Six Stages of Disease, or sometimes referred to as Six-Channel patterns, mentioned in the Shang Han Lun. The function of the Defense-Wei-Qi is to protect us against the invasion of Pathogenic Factors. If Defense-Wei-Qi is strong and the six Qi are not excessive or untimely, we are protected against the invasion of Pathogenic Factors. If the Defense-Wei-Qi is weak or the climate is excessive, Pathogenic Factors can invade the organism and cause disease. Patients who already suffer from internal patterns involving cold, heat, dampness, dryness or wind, are often more sensitive to external factors. For example, patients suffering from Damp-Cold in the Spleen will be especially sensitive to damp-cold climate while patients with inner Heat will show an aversion to hot climate. The Defense-Wei-Qi tries to prevent an invasion of the Pathogenic Factors into the deeper levels of the body. Therefore, the fight against these factors takes place on the body-surface. A defense reaction of the body is fever. Fever opens the pores so that the surface is released and the Pathogenic Factor is expelled through perspiration. If this process is not successful, the Pathogenic Factor penetrates the body deeper and can damage the Zang Fu organs. The Five-Element theory assigns a particular Pathogenic Factor to each of the five Zang-Fu organs, but this is more a relative than an absolute assignment. E.g. Dryness is assigned to the Lungs and the Lungs are also susceptible to Dryness. But the Lungs are exposed to all Pathogenic Factors because, as the most exterior organ, the Lungs have the closest contact to the outside world. External circumstances that enable the Pathogenic Factors to invade the body include extreme climates, or job related conditions (for example, working with a lot of heat and fire at a blast furnace), as well as the excessive use of air-conditioners or heaters. Excessive physical activity can sometimes cause the Pathogenic Factor to invade the body. The explanation here is that physical activity causes Heat. Heat opens the pores and perspiration occurs in order to cool the body. If the perspiration is excessive, cold, which is caused by evaporation, can penetrate the body and accumulate. Therefore Cold may also appear in summer. Sometimes these Pathogenic Factors play a major role in pains or aches that are difficult to treat. A deficient Defense-Wei-Qi is the main factor regarding the endogenous cause of disease. Therefore, all organs that are involved in the production of Defense-Wei-Qi have to be considered: Kidney, Spleen and Lungs. Further causes of Defense-Wei-Qi deficiency are a Spleen-weakening diet that includes large amounts of cold meals, frozen food, food prepared in the microwave or fast food. |

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