In TCM the main pathologic change in diarrhea is in the spleen, the stomach and the intestines, but is also related to the liver and the kidney. Spleen insufficiency with ascendancy of Dampness is the key to the development of diarrhea. The exogenous causes are most intimately related to Dampness. When Dampness invades and injures the spleen and the stomach, their transportation and transformation functions are impaired. Hence Plain Questions states: "When Dampness wins, diarrhea ensues."

The endogenous causes are most intimately related to insufficiency of the spleen. An insufficient spleen fails in its functions, so that the essences of foods and drinks cannot be extracted. Endogenous Dampness and turbidity result; and the descent of the mishmash of undigested foods and turbidity descend and lead to diarrhea. In the Collected Works of Zhang Jingyue it is stated: "The basic pathology of diarrhea is no other than the spleen and the stomach." Even diarrhea due to liver or kidney dysfunction develops primarily on the basis of impaired spleen and stomach function.