The theoretical framework of Traditional Chinese Medicine (TCM) is centered around the five organs, with physiological foundations based on Yin, Yang, Qi, Blood, Body Fluids, and Essence. Throughout history, TCM has accumulated a vast amount of literature, covering aspects from the environment to the human body, from etiology to pathogenesis, and from syndromes to treatment methods and herbal formulas. Due to its unique developmental process, many theories and concepts in TCM lack stable connotations, a phenomenon particularly evident in the concepts related to internal dampness. The concepts associated with internal dampness are all related to the metabolic disorders of body fluids, including water, phlegm, and fluid. These four have many correlations and can sometimes act together to cause disease, which is the main reason for conceptual overlap and confusion. In special circumstances, it can be difficult to distinguish and define them; however, there are still clear differences in their sources and natures. As stated in the Suwen: On the Differentiation of Meridians (Chapter 21): “When food Qi enters the stomach, it disperses essence in the liver and moistens the tendons. Food Qi enters the stomach, turbid Qi returns to the heart, and essence is moistened in the vessels. The Qi flows through the meridians, and the meridian Qi returns to the lungs, which distribute essence to the skin and hair. The hair vessels combine with essence, circulating Qi in the organs… Fluid enters the stomach, travels and overflows essence, and is transported to the spleen, where spleen Qi disperses essence, returning to the lungs; it regulates the waterways and is discharged to the bladder. Water and essence are distributed, and the five meridians operate together.” This scripture has been repeatedly cited by later physicians to illustrate the process and pathways of body fluid metabolism. The Neijing summarizes this from a relatively general perspective, but in reality, the metabolism of body fluids is very complex, evolving into various functional liquid substances or functional states through the operation of the body’s organs and meridians.
In the Ling Shu: On the Five Types of Body Fluids (Chapter 36), it states: “The Yellow Emperor asked Qi Bo: When food and drink enter the mouth and are transported to the intestines and stomach, their fluids are differentiated into five types. In cold weather, with thin clothing, it results in urination and Qi; in hot weather, with thick clothing, it results in sweating; when sorrowful Qi combines, it results in tears; when the stomach is warm and relaxed, it results in saliva. When pathogenic Qi reverses internally, it obstructs Qi and does not flow; when it does not flow, it results in water retention. I know this is the case, but I do not know how it arises. I wish to hear about its principles.” Qi Bo replied: “All food and drink enter the mouth, and their flavors are five, each entering their respective seas. Body fluids each follow their pathways, thus the Sanjiao (Triple Burner) emits Qi to warm the muscles and nourish the skin, which is its essence; that which flows but does not move is liquid.” In cold weather, the pores close, causing Qi and dampness to stagnate, and water remains in the bladder, resulting in urination and Qi. These statements propose further differentiation after food enters the stomach, indicating that under normal physiological conditions, it transforms into Qi, excretes as sweat, reverses as tears, discharges as urine, flows as essence, and retains as liquid. In pathological conditions, cold can cause pain from accumulation, and obstruction can lead to water retention. These are merely the easily perceivable phenomena. The physiological and pathological processes of complex body fluid metabolism in different parts of the body should be even more intricate and profound. The macro-level distinctions among these four have historically been a topic of research for scholars and physicians.
The Neijing states that “the kidneys govern water” and “the spleen governs dampness,” which is a conclusion derived from the classification of the five elements. In the Ling Shu: On Pathogenic Factors, it states: “When the five grains enter the stomach, their residues, body fluids, and essence are divided into three pathways.” Here, body fluids refer to the subtle substances within food and drink. In the Ling Shu: On the Decision of Qi, it states: “The upper burner opens, dispersing the essence of the five grains, nourishing the skin and filling the body like mist and dew; this is called Qi. What is essence? Qi Bo said: When the pores open and sweat flows, this is called essence. What is liquid? Qi Bo said: When grains enter and Qi is full, it seeps into the bones, nourishing the marrow and moistening the skin; this is called liquid. What is blood? Qi Bo said: The middle burner receives Qi and extracts essence, transforming it into red blood; this is called blood.” Qi, essence, liquid, and blood are differentiated from one another: In the Ling Shu: On the Five Types of Body Fluids, it states: “All food and drink enter the mouth, and their flavors are five, each entering their respective seas. Body fluids each follow their pathways, thus the Sanjiao emits Qi to warm the muscles and nourish the skin, which is its essence; that which flows but does not move is liquid.” In the Ling Shu: On Pathogenic Factors, it states: “Nourishing Qi secretes its essence and injects it into the vessels, transforming it into blood to nourish the four extremities.” Qi, essence, liquid, and blood are interrelated and can transform into one another; thus, the generation of phlegm, fluid, water, and dampness is related to all four. The Suwen: On the Secret of the Linglan states: “The bladder is the official of the metropolis, where body fluids are stored; when Qi transforms, it can be released.” The Suwen: On Reversal Regulation states: “The kidneys are the water organ, governing body fluids,” exploring the relationship between the organs and body fluids from different aspects.
Although body fluids are governed by multiple organs, the generation of phlegm, fluid, water, and dampness still has clear distinctions. From the aforementioned definition of dampness, dampness is the state of water and liquid being stagnant and infiltrating, formless yet having signs. Therefore, its source should be the essence that cannot be distributed. Since the spleen is the main organ for transporting body fluids, it is logical to say that the spleen governs dampness; however, this does not imply that dampness has no other causes. From the above reasoning, the pathways for dampness generation should be numerous, differing only in etiology, pathogenesis, and clinical conditions. The Neijing: On the Great Discussion of the Six Origins (Chapter 71) states: “When dampness is excessive, it moistens and leaks; if severe, it leads to water retention and swelling,” indicating that excessive dampness manifests externally as water diseases causing swelling. Water is visible, presenting as edema symptoms. In the Neijing, the kidneys and urination are not directly related; however, there is the viewpoint in the Suwen: On Reversal Regulation: “The kidneys are the water organ, governing body fluids.” The Suwen: On Water and Heat Points states: “Do all waters originate in the kidneys? Qi Bo said: The kidneys are the female organ; the earth’s Qi rises to the kidneys, producing water and body fluids.” “How can the kidneys gather water and cause disease?” Qi Bo said: “The kidneys are the gate of the stomach. If the gate is not functioning well, water accumulates and follows its kind. It overflows to the skin, resulting in swelling. Swelling is caused by water accumulation and leads to disease.” From this perspective, water originates in the kidneys, resulting from the overflow of body fluids. The overflow and accumulation of body fluids are not solely related to the kidneys. The Suwen: On the Discussion of the Five Qi (Chapter 23) states: “The lower burner overflows as water.” The Ling Shu: On the Five Types of Body Fluids states: “When the pathways of Yin and Yang are obstructed, the four seas are blocked, the Sanjiao does not drain, and body fluids do not transform, food and drink flow through the intestines and stomach, separated in the ileum, remaining in the lower burner, unable to permeate the bladder, leading to lower burner distension; when water overflows, it results in water retention.” This indicates that the Sanjiao not draining and meridians being obstructed can still produce water, but the water generated in a localized area has a different name. The Suwen: On the Great Discussion of the True Essentials states: “When the Taiyin is excessive… the head is heavy, the legs and feet swell, fluid accumulates internally, and swelling occurs above.” The Suwen: On the Great Discussion of Qi Transformation states: “When the earth element is excessive, dampness flows, and kidney water is affected. People suffer from abdominal pain, clear and cold feelings, heaviness, and discomfort, with severe cases leading to muscle atrophy, foot weakness, and pain in the feet, with fluid accumulation and reduced appetite, and limbs unable to lift.” The Suwen: On the Great Discussion of the True Essentials states: “People suffer from fluid accumulation, causing heart pain.” Combining this with the discussion in the Jin Gui Yao Lue: On Phlegm and Fluid Diseases, fluid refers to the pathological changes where body fluids are retained in a localized area, which can include dampness or can transform into water. This is mainly related to the obstruction of local meridians. The concept of phlegm does not appear in the Neijing, but first appears in the Jin Gui Yao Lue: On Coughing and Wheezing Diseases: “Phlegm obstructs the upper, causing fullness, wheezing, coughing, and spitting…” and the concept of “phlegm and fluid cough” is not specifically discussed, with the former referring to thick saliva and the latter to “thin.” The On the Sources of Various Diseases (Volume 20: On Phlegm and Fluid Diseases) states: “Phlegm and fluid arise from Qi obstruction, where body fluids do not flow, and water and fluid stagnate in the chest, forming phlegm,” and “all phlegm arises from blood vessel obstruction, where water accumulates and does not disperse, thus forming phlegm. It can be cold, hot, solid, or due to undigested food, or cause fullness in the chest and abdomen, or shortness of breath and good sleep; the symptoms are not singular, hence the term ‘various phlegm.'” Although phlegm is discussed as being caused by Qi obstruction, phlegm and fluid are still not distinguished. The On the Sources of Various Diseases (Volume 3: On Phlegm and Fluid Symptoms) states: “Phlegm is the accumulation of saliva in the chest; fluid is the accumulation of water in the bladder.” This is the earliest form of distinction, but essentially, it differentiates between phlegm that is coughed up and fluid accumulation in the lower burner. After the Song, Jin, and Yuan dynasties, new names for phlegm and fluid emerged, distinguishing clear and thin as fluid and thick and turbid as phlegm. This marked a shift in the theory of phlegm disease becoming independent from fluid disease theory. Yang Renzhai in the Ren Zhai Zhi Zhi Fang Lun has already listed “phlegm and saliva” alongside “water and fluid” in the table of contents, indicating that the theory of phlegm disease gradually became independent from fluid disease theory: “When a person’s Qi and blood are clear and smooth, body fluids flow freely; how can there be phlegm? Only when Qi and blood are turbid and reversed do body fluids become unclear, steaming and accumulating into phlegm.” “If phlegm is caused by fire rising, and lung Qi is not clear, it causes coughing at times, and old phlegm or stagnant phlegm forms sticky lumps, obstructing the throat, making it difficult to expel; these types of phlegm are all caused by fire evil rising, steaming in the upper burner, and lung Qi being obstructed, thus the body fluids that rise with Qi become steamed and condensed, deeply rooted over time, hence named old or stagnant, with the source being fire evil. The disease is located between the upper burner heart and lungs, and the throat, not comparable to the middle burner spleen and stomach’s warm phlegm, cold phlegm, phlegm and fluid, or phlegm and saliva.” “When Qi and blood are turbid and reversed, body fluids become unclear, steaming and accumulating into phlegm,” indicating that “steaming and accumulating” implies that the evil Qi causing the steaming should naturally be fire evil. However, the Ren Zhai Zhi Zhi Fang proposes that “if phlegm is caused by fire rising… these types of phlegm are all caused by fire evil rising, steaming in the upper burner… not comparable to the middle burner spleen and stomach’s warm phlegm, cold phlegm, phlegm and fluid, or phlegm and saliva.” Thus, fire evil rising phlegm is only one type of phlegm, which must be distinguished from warm phlegm, cold phlegm, phlegm and fluid, and phlegm and saliva. Zhang Jingyue summarized in the Complete Book of Phlegm and Fluid: “Although phlegm and fluid are said to be of the same category, they are actually different… fluid is clear and thin while phlegm is thick and turbid.” Subsequently, physicians further distinguished phlegm and fluid based on disease location, believing that fluid evil often remains localized, while phlegm can be found everywhere. Zhang Jingyue also stated: “Fluid only accumulates in the intestines and stomach, while phlegm can be found everywhere. When food and drink do not transform and remain as fluid, the disease is entirely due to the spleen and stomach; phlegm, which can be found everywhere, can arise from injuries to any of the five organs.” Most physicians’ discussions on phlegm have been limited to this. The Yi Zong Bi Du states: “The spleen is the source of phlegm generation,” and “only when the spleen is deficient and damp can the clear rise and the turbid descend, remaining stagnant and accumulating, thus forming phlegm.” This provides a new perspective on the generation of phlegm, with the Qing dynasty’s Wang Bichang in the Yi Jie Bian Zheng clearly distinguishing the pathogenesis of phlegm and fluid, stating: “Phlegm is generated from essence; fluid is transformed from water.” Thus, the source of phlegm has a clear viewpoint and is distinctly separated from fluid, indicating that phlegm is formed from the accumulation of essence and liquid. Qi, blood, body fluids, and essence have a certain form of mutual transformability; thus, if Qi and blood become phlegm, they must first transform into turbid. The above analysis can serve as the basic principles for distinguishing phlegm, fluid, water, and dampness in the literature.
Treatment: For diseases of phlegm and fluid, one should warm and harmonize, using formulas such as Ling Gui Zhu Gan Decoction and Er Chen Decoction, which can be adjusted as needed.
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