The theory of traditional Chinese medicine is based on the five internal organs, and it is believed that health preservation is to nourish the five internal organs. Therefore, the different forms of water in five zang-organs are summarized as sweat as heart fluid, tears as liver fluid, saliva as spleen fluid, nasal discharge as lung fluid and saliva as kidney fluid, which are collectively called five fluids of human body.

Khan (pinyin: hàn, hán) is a first-class standard Chinese character (commonly used word). This word first appeared in Shi Guwen, the state of Qin in the Eastern Zhou Dynasty. The original meaning of "sweat" refers to the liquid secreted by sweat glands of human beings and some animals. The bamboo slips written in ancient times are called Historical Records because they have to be baked with fire first, so that the water in the bamboo slips can seep out like sweat, and after drying, it is easy to write without being eaten by insects. Sweat is the liquid discharged by the human body through the pores on the skin surface, which comes from the theory of visceral suppression in Yu Su's collected works.