Phlegm is the mucus expelled by the lungs and airways. Thick and turbid phlegm is termed tan (痰), while clear and thin phlegm is referred to as yin (饮). Both are considered tangible forms of phlegm. The formation of phlegm is primarily due to the disharmony of the organs’ qi and blood, as well as the condensation of dampness and body fluids. It is a product of pathological changes in the organs, particularly a pathological product resulting from disorders in the body’s water and fluid metabolism. However, it can also become a pathogenic factor for other diseases.
According to the Jingyue Quanshu (《景岳全书·痰饮》), “Phlegm is essentially the body’s body fluids, transformed from the essence of food and water. This phlegm is a transformed substance, not something that does not transform. If the transformation is correct, the body is strong, and the nutritive and defensive qi are abundant. Phlegm and saliva are both derived from blood and qi. If the transformation is incorrect, it leads to organ disease, fluid failure, and blood and qi turning into phlegm and saliva.” The production of phlegm is closely related to the lungs, spleen, and kidneys. Under normal circumstances, the essence of food and water is transformed through the San Jiao (三焦) into either jin (津) or xue (血) to nourish the entire body; useless substances are transformed into sweat, qi, or urine and expelled from the body, thus preventing the formation of phlegm. Only when the body is invaded by external pathogens or suffers internal injuries from emotions, dietary indiscretions, fatigue, or inappropriate lifestyle factors, leading to the loss of normal biochemical distribution functions of the lungs, spleen, and kidneys, and impaired transformation in the San Jiao, does the essence of food and water fail to transform properly, gradually accumulating into phlegm, which can then lead to various pathological conditions. As stated in the Zhengzhi Huibian (《证治汇补·痰证》), “The qi pathways of a person should be clear and smooth; thus, the body fluids flow freely, and there should be no phlegm. If invaded by external wind, heat, dryness, or dampness, or disturbed internally by fright, anger, worry, or overthinking, along with dietary indiscretions, excessive drinking, and lack of clarity in the nutritive and defensive qi, the qi and blood become turbid and fail, leading to the generation of phlegm.” However, due to the varying nature of the external pathogens and the duration of the disease, the color and odor of phlegm can also differ. Clinically, we can assess the cold-heat, deficiency-excess, and duration of the disease based on the color and odor of the phlegm. As noted in the Zhibing Yuanliu Xizhu (《杂病源流犀烛·痰饮源流》), “Fresh and light phlegm has a bland taste and is clear and thin; while chronic and heavy phlegm is yellow, turbid, thick, and sticky, difficult to expel, gradually developing into a foul taste, with sour, spicy, fishy, salty, bitter flavors, and even blood may be present.”
① Fishy Phlegm
[Olfactory Diagnosis] The patient coughs up white, clear, and thin phlegm, which has an unusually fishy odor.
[Clinical Significance] Fishy phlegm is often associated with deficiency-cold syndromes. Commonly seen in patients with late-stage asthma and deficiency of yang in the spleen and kidneys.
[Treatment Method] It is advisable to warm yang and dispel cold, using formulas such as Fu Zi Li Zhong Wan (附子理中丸) and Jin Gui Shen Qi Wan (金匮肾气丸) with modifications.
② Foul-smelling Phlegm
[Olfactory Diagnosis] The patient coughs up turbid phlegm, and in severe cases, coughs up pus and blood, with a strong foul odor.
[Clinical Significance] Foul-smelling phlegm is often caused by lung abscesses. If the phlegm has a particularly foul odor, it may indicate lung abscess, bronchiectasis, or late-stage malignant lung tumors.
[Treatment Method] It is advisable to clear the lungs, transform phlegm, and resolve abscesses and toxins, using Qian Jin Wei Jing Tang (千金苇茎汤) with modifications.
③ Bitter Foul Phlegm
[Olfactory Diagnosis] The patient coughs up thick phlegm with a bitter foul odor.
[Clinical Significance] This is often associated with heat-type coughs, such as those caused by external pathogens entering the interior and transforming into heat, leading to lung heat cough.
[Treatment Method] It is advisable to clear the lungs and transform phlegm, using Qing Jin Hua Tan Tang (清金化痰汤).
④ Sweet Phlegm
[Olfactory Diagnosis] The patient coughs up mostly white phlegm with a sweet taste.
[Clinical Significance] This is indicative of spleen deficiency with stagnant dampness, leading to phlegm that invades the lungs.
[Treatment Method] It is advisable to strengthen the spleen, resolve dampness, transform phlegm, and stop cough, using Si Jun Zi Tang (四君子汤) combined with Er Chen Tang (二陈汤) with modifications.
⑤ Sour and Spicy Phlegm
[Olfactory Diagnosis] The patient coughs up yellow, sticky phlegm with a sour and spicy taste.
[Clinical Significance] This is often due to liver fire invading the lungs, leading to the lungs losing their ability to clear and regulate.
[Treatment Method] It is advisable to pacify the liver, reduce fire, clear the lungs, and stop cough, using Xie Bai San (泻白散) combined with Dai He San (黛蛤散).
⑥ Salty Phlegm
[Olfactory Diagnosis] The patient coughs up thin, white phlegm with a salty taste.
[Clinical Significance] This is often caused by kidney deficiency cough.
[Treatment Method] It is advisable to warm the kidneys, transform phlegm, and stop cough, using Jin Gui Shen Qi Wan (金匮肾气丸) with modifications.
