TCM pays great attention to the role of healthy qi in causing disease. It believes that normal visceral functions, superabundance of healthy qi, exuberance of qi and blood, and compactness of the defensive qi will prevent pathogenic factors from invading the body. That is why Huangdi Neijing says that "with sufficient healthy qi inside the body, pathogenic factors will have no way to invade the body". Only when healthy qi becomes deficient and the defensive qi is weakened can pathogenic factors invade the body, leading to disorder of yin and yang in the body, disturbance of the visceral functions and occurrence of disease. That is why Huangdi Neijing says that "if pathogenic factors invade the body, qi in the body must be deficient." Obviously TCM emphasizes the role of healthy qi in causing disease.

       

Insufficiency of healthy qi is responsible for invasion of pathogenic factors into the body. However, insufficiency of healthy qi manifests in different ways, including general insufficiency and local insufficiency as well as constant insufficiency and temporary insufficiency. General insufficiency usually leads to general disease or transmission of pathogenic factors from local region to other areas. Local insufficiency leads to local disease that will not be transmitted to other areas. Constant insufficiency is usually marked by weak constitution that gives rise to frequent invasion of pathogenic factors and frequent occurrence of disease. Temporary insufficiency is usually due to fatigue, hunger, mental impairment, sexual intercourse, menstruation and labor, though the constitution is usually strong.

Pathological changes may vary due to different degrees of insufficiency of healthy qi and invasion of pathogenic factors. Generally speaking, pathological changes are serious if insufficiency of healthy qi is severe and pathological changes are mild if insufficiency of healthy qi is light. The state of pathological changes is related to the struggle between healthy qi and pathogenic factors. If insufficiency of healthy qi is severe, it will be weak in fighting against pathogenic factors, leading to deficiency syndrome or syndrome of deficiency mingled with excess. If insufficiency of healthy qi is not very serious, it will be strong enough to fight against pathogenic factors, usually leading to excess syndrome due to severe struggle between healthy qi and pathogenic factors.