Traditional Chinese medicine theory holds that the internal environment of the human body is composed of substances such as qi, blood, and body fluids. Among them, body fluid is a collective term for all fluids in the human body, including saliva, sputum, snot, tears, etc. In traditional Chinese medicine, phlegm and yin are pathological products formed by abnormal stagnation of body fluids in the human body.
Thick and turbid substances are called phlegm because their texture is relatively thick and difficult to expel from the body. The formation of phlegm can cause certain harm to the human body, as it can block the airways, affect normal respiratory function, and also breed bacteria and viruses
中医理论认为，人体的内部环境是由气、血、津液等物质所构成的。其中，津液是人体内所有液体的统称，包括唾液、痰涎、鼻涕、泪液等。在中医中，痰和饮都是人体内津液异常停滞所形成的病理产物。

稠浊的物质被称为痰，这是因为它们的质地较为浓稠，难以被排出体外。痰的形成会对人体造成一定的危害，因为它会阻塞气道，影响正常的呼吸功能，同时也会滋生细菌和病毒.