The causes of asthma include internal and external factors. The internal factor lies in the retention of phlegm and fluid inside the body. The retention of phlegm results from the deficiency of the lung, spleen and kidney. The fluid metabolism of the human body is closely related to the lung, spleen and kidney. The normal fluid metabolism of human body depends on the dispersing and descending functions of the lung, the transporting and transforming functions of the spleen and the warming function of the kidney.

If lung qi is deficient, the lung will fail to disperse and descend, and distribute, resulting in phlegm transformed from the accumulated liquid; if the spleen qi is deficient, the spleen will fail to transport and transform water and food, causing phlegm transformed from the accumulated dampness; if the kidney qi is deficient, the kidney will fail to perform its qi activity, giving rise to phlegm transformed from the excessive water due to kidney yang deficiency in evaporation. When the kidney yin is deficient, the internal heat will burn the body fluid and make it phlegm. The external factors of the disease mainly include the six exogenous pathogenic factors with wind-cold and wind-heat being the major ones. If exogenous pathogenic factors invade the lung, the lung will fail to disperse and descend, causing reversely rising qi inter- mingled with latent phlegm.

In this case, phlegm and qi jointly obstruct the lung, developing into asthma. Besides, if people contact special objects like pollen, lamp- black, hairy dust, etc., or if internal food injury like overingestion of raw, cold, salty and sour food occurs, the regulating qi and blood, dredging water passages and dispersing and desending of the lung, the transporting,transforming and distributing of the spleen will be affected, giving rise to the disorder of qi in ascending and descending. In this case, the latent phlegm is disturbed and rises with the rising qi, developing into asthma. In short, the onset of asthma is the result in which the external causes exert influence on the internal ones.