The human body is endowed with ability to resist the invasion of various kinds of pathogenic factors so as keep a relative balance in the interior of the body as well as between the human body and the environmental conditions. This ability is called anti-pathogenic Qi. The various pathogenic factors that can break either of the two states of relative balance are called pathogenic Qi. The normal co- ordination of yin and yang in the body is destroyed and an abnormal change of preponderance or discomfiture of either yin or yang results. Exposure to the wind after seating, or sleeping in a draught, are important inducting factors in being affected by pathogenic wind.
Pathogenic cold is prevalent in winter, as are diseases of cold.
In the cold season, too little clothing, exposure to cold after sweating, and being caught in wind and rain provide chances for the development of pathogenic cold. Diseases caused by pathogenic summer heat occur only in summer. Onset is often due to prolonged exposure to blazing sun on hot days, or staying in a hot room with poor ventilation. Damp Pathogenic damp occurs mainly in the late summer rainy season. Such diseases usually follow the wearing of clothing wet with rain or sweat, dwelling in low-lying and damp place, or being in frequent contact with water during work.