TCM defines a healthy person as one whose Yin and Yang are balanced. Such a balance exists in the person’s viscera, meridians, Qi, Blood, body fluid, and between the person and his or her environment. Disease breaks out when the balance is disturbed by pathogens. An outbreak depends on the pathogen type and healthy Qi strength (body resistance). The personal constitution also determines the outcome of a pathogen attack.
Disease is the outcome of the struggle between pathogens and healthy Qi. The struggle begins between a body with compromised healthy Qi, and the intrusion of pathogens. It continues throughout the entire disease process.
(1)The body is constituted, and chiefly maintained, by healthy Qi. Qi exists in all internal organs and meridians, and ensures their normal functions. When pathogens invade, healthy Qi defends and protects the body from illness.
(2)To successfully defend against pathogens, the body needs ample healthy Qi. The quantity of healthy Qi is determined by Kidney-Qi (congenital) and Spleen–Stomach Qi (acquired after birth). In TCM, the body’s major elements are interchangeable, including Qi, essence, blood, body fluid, Yin and Yang. The abundance of any one directly influences the abundance of healthy Qi. When healthy Qi is insufficient, the body’s defense against pathogens is weakened, and the chance of illness increased.
(3)Pathogens directly disturb the normal physiological functions of the body, and include six abnormal climatic factors, seven emotional irregularities, pestilence, diet, overtiredness, blood stasis, rheum, etc. A body deficient in healthy Qi is vulnerable to pathogens, also called “deficiency pathogens.” Huangdi Neijing states, “When two conditions of deficiency combine, pathogens begin to attack the body.”