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The Eight Principles (八纲) refer to the eight categories of syndromes: Yin, Yang, Exterior, Interior, Cold, Heat, Deficiency, and Excess. The differentiation based on these principles is the most fundamental method of diagnosis and treatment in Traditional Chinese Medicine (TCM). In his work “Medical Insights,” Qing Dynasty scholar Cheng Zhongling stated: “Diseases fundamentally revolve around these eight terms: Cold, Heat, Deficiency, Excess, Exterior, Interior, Yin, and Yang. If the disease does not fall outside of these, then the method of differentiation will not stray from this.” The imbalance of Yin and Yang leads to a state of Deficiency or Excess, while Cold and Heat are the most direct manifestations of this state. During clinical inquiries, the question of “Cold and Heat” is always prioritized.
Definition of Cold and Heat
Cold and Heat have two layers of meaning: one refers to the symptoms of Cold and Heat, and the other to the pathophysiological mechanisms of Cold and Heat. First, regarding the symptoms of Cold and Heat: Cold encompasses symptoms of weakness such as aversion to cold, cold limbs, poor spirit, spontaneous sweating, and diarrhea; Heat refers to symptoms of excess such as fever or subjective feeling of heat, aversion to heat, irritability, internal heat, dry stools, and foul breath. The “Huangdi Neijing” states: “When Yang prevails, there is Heat; when Yin prevails, there is Cold.” “Medical Insights” summarizes the manifestations of Cold and Heat as follows: “The Cold and Heat of a disease is entirely reflected in thirst or lack of thirst, whether one can or cannot retain fluids, preference for hot or cold food, irritability or reversal of Qi, the frequency and color of urination, the consistency of stools, and the pulse being slow or rapid. If one is thirsty and can retain fluids, prefers cold food, is irritable, has short and red urination, and has hard stools with a rapid pulse, this indicates Heat. Conversely, if one is not thirsty, or is falsely thirsty and cannot retain fluids, prefers hot soup, has cold hands and feet, has clear and frequent urination, has loose stools, and a slow pulse, this indicates Cold.”Secondly, regarding the pathophysiological mechanisms of Cold and Heat, the “Neijing” states: “Cold causes Qi to contract, while Heat causes Qi to disperse.” It also states: “Cold causes the pores to close, preventing Qi from circulating, hence Qi contracts. Heat opens the pores, allowing the Wei and Ying Qi to communicate, leading to excessive sweating, hence Qi disperses.” Cold causes Qi to contract, while Heat causes Qi to disperse; Cold causes the pores to close and prevents sweating, leading to a tendency towards Excess; Heat opens the pores, causes excessive sweating, leading to a tendency towards Deficiency. Here, Cold and Heat correspond to the concepts of “injury from Cold” and “Wind” frequently used in the “Shanghan Lun” (Treatise on Cold Damage). Cold represents contraction and Excess, while Heat or Wind represents dispersion and Deficiency, which differs from the common understanding that Cold is often Deficient and Heat is often Excessive. The “Shanghan Lun” and “Jinkui Yaolue” provide numerous examples utilizing the principles of Cold contraction and Heat dispersion. In cases where Cold and Heat are not clearly understood, some may seem counterintuitive. For instance, after taking the Sanwu Baisan formula, it is noted: “If one cannot tolerate hot porridge, and diarrhea does not stop, then take a cup of cold porridge.” The “Jinkui Yaolue” states: “If diarrhea persists, drinking a cup of cold water will stabilize it.” This applies the principle of Cold contraction to address excessive sweating and diarrhea. Similarly, after taking Guizhi Decoction, it is advised to “sip hot porridge to assist the medicinal effect,” and after taking Wuling San, “drink warm water to promote sweating for recovery,” utilizing the characteristics of Heat dispersion to treat conditions such as lack of sweating, difficulty urinating, and overall Qi stagnation. In summary, for diseases characterized by Qi stagnation, Heat helps to disperse, while Cold helps to consolidate in cases of excessive dispersion. Therefore, warming herbs like Ma Gui are used to disperse, while cooling herbs like Bai Hu are used to consolidate. The “Neijing” states: “To disperse the exterior, do not stray far from Heat; to attack the interior, do not stray far from Cold.” In my clinical practice, I often encounter patients who experience diarrhea the day after consuming spicy food, which is due to the internal presence of Damp-Heat; the spiciness triggers the diarrhea, indicating that Heat leads to Qi dispersion.
Transformation of Cold and Heat
The “Suwen: Water and Heat Acupuncture” states: “The Emperor asked: Why does injury from Cold lead to Heat? Qi Bo replied: When Cold is excessive, it generates Heat.” The “Suwen: Heat Discussion” states: “All Heat diseases are a result of Cold injury.”Heat leads to Qi dispersion, and Qi dispersion leads to Deficiency, hence the aversion to Cold. Cold leads to Qi contraction, and Qi contraction leads to Excess, hence the appearance of fever. Although termed “injury from Cold,” the symptoms manifest as severe fever; the more severe the Cold exposure, the more intense the fever. Cold and Heat are not as opposed as ice and fire; rather, they transform into one another and are mutually causal. “When Cold is excessive, it generates Heat” may seem counterintuitive, leading later physicians to interpret it as “internal transformation into Heat.” As long as one understands that “Cold causes Qi to contract, and Heat causes Qi to disperse,” it can be understood that Cold stagnation will inevitably generate Heat, and Heat is generally caused by Cold. This is why the “Suwen: Heat Discussion” states: “All Heat diseases are a result of Cold injury.” The discussion in the “Shanghan Lun” regarding the Taiyang Cold Injury syndrome, whether it has already manifested as fever or not, follows this principle: there is an external cause of Cold exposure, which subsequently leads to exterior Heat appearing, and further development may result in both exterior Cold and interior Heat, or both being Excessive, where the treatment method initially employs Ma Huang Tang followed by the emergence of Da Qinglong Tang syndrome, Xiao Qinglong Jia Shigao Tang syndrome, and Xiao Chaihu Jia Shigao Tang syndrome. Although the summer-heat syndrome is classified as Heat, it often presents with a deficiency of body fluids; thus, cooling formulas such as Qing Shu Yi Qi Tang and Bai Hu Jia Ren Shen Tang often contain tonifying herbs, as stated in the “Neijing”: “When Qi is abundant, the body is Cold; when Qi is Deficient, the body is Hot;” Liu Wansu in “Suwen: Mysteries of Disease” analyzed the relationship between Cold and Heat, stating: “The classics say: ‘When a person is injured by Cold, it results in Heat.’ This is because Cold injures the skin and hair, causing the pores to close tightly, leading to stagnation of Yang Qi, which cannot circulate, resulting in Heat. Therefore, when there is Heat on the surface due to Cold injury, it is Heat at the surface. It is advisable to use Ma Huang Tang or similar sweet, pungent, and warming herbs to disperse, allowing the pores to open, sweating to release Heat, and thus recover. Any internal injury from Cold substances may lead to Yin prevailing over Yang, resulting in Cold disease; or Cold and Heat may clash, causing stagnation of Yang Qi in the stomach and intestines, resulting in Heat; or there may be internal injury from Cold substances leading to Heat, resulting in profuse sweating and cooling of the body, or mild symptoms that do not lead to other diseases, merely resulting in sourness in the stomach, commonly referred to as ‘vinegar heart.’ The treatment should involve warming herbs to disperse, similar to the meaning of resolving the exterior, to open the stagnation in the stomach and intestines, allowing the Heat to disperse and harmonize. If one has long enjoyed sour foods without cessation, warming is not advisable; rather, cold herbs should be used to purge, followed by cooling herbs to adjust, allowing the Heat to dissipate and Qi to harmonize. Therefore, sour foods should not be consumed with sticky, greasy foods, as this can lead to stagnation and blockage of Yang Qi. For example, if food is left in a container, it becomes heated and sour. It is advisable to consume vegetables, which can promote the smooth flow of Qi.Liu’s analysis aligns closely with the principles of the “Neijing”; no wonder later generations refer to him as the “Master of Heat Diseases.”From the above discussion, one can relate it to the first law of thermodynamics in physics, also known as the law of conservation of energy. It simply states that “energy cannot be created or destroyed; it can only change from one form to another or transfer from one object to another, while the total amount of energy remains constant.” Humans are warm-blooded animals with self-regulating mechanisms that always strive for a general stability of energy. When excessive energy enters the body, it must find ways to expel it, striving for a balance of input and output, such as through fever, sweating, and urination; there may also be symptoms like irritability and insomnia, which are ways to expel energy through activity and emotions; or symptoms like rashes and ulcers, which release energy through the skin; or through tears, nocturnal emissions, and menstrual flow to expel energy. Energy that cannot be expelled in time is temporarily stored in the form of fat, leading to obesity. Excessive energy entering the body does not simply disappear; it can only be expelled from the body or presented in another form, which manifests as physiological expressions or pathological symptoms, often as a result of the body’s feedback compensation mechanism attempting to restore energy balance. Therefore, pathological symptoms that appear in the body cannot simply be countered to make them disappear; rather, one must trace back to the source and clear the root cause. Internal Heat can lead to loose stools and increased frequency, as the body increases the frequency of bowel movements to alleviate internal Heat; one cannot use astringent herbs to stop diarrhea for two reasons: first, such diarrhea is difficult to stop; second, as soon as the diarrhea slightly alleviates the internal Heat, it will seek another outlet, possibly manifesting as sore throat, excessive sweating, irritability, etc. Therefore, this type of diarrhea should be treated with purgative and clearing herbs.Cold and Heat are merely external manifestations of disease; the statement “Cold is Heat, and Heat is Cold” cannot be universally applied and requires accurate differentiation. For example, Zhang Zhongjing’s warming herbs can eliminate great Heat, Li Dongyuan’s sweet warming herbs can eliminate great Heat, or Liu Wansu’s pungent cooling and cold herbs can resolve Heat, while Wang Taifu’s strong water can support fire. The essence of disease lies in the balance of Yin and Yang; only by understanding the dynamics of Yin and Yang and not being misled by appearances can one accurately identify the source of the disease and apply the correct treatment.Written by: Zhen Weishuai, People’s Hospital of Lixia District, Jinan City, Shandong ProvinceEditor: Xu JingReviewed by: Li Xiuyun, Bai Xiaoyun