The concept and classification of etiology: The causes that lead to diseases in the human body are referred to as etiology, also known as “pathogenic factors,” “pathogens” (historically referred to as “disease sources”), and “evil pathogens.” Diseases are pathological processes caused by pathogenic factors under certain conditions, including the forms of onset, pathogenesis, development patterns, and outcomes. After the pathogenic factors act on the human body, they disrupt the physiological state, leading to certain disorders, obstacles, or damages in morphology, function, and metabolism. In other words, etiology refers to specific factors that can disrupt the dynamic balance of human physiology and cause diseases. Etiological factors include the six excesses, epidemics, seven emotions, diet, overwork, external injuries, as well as phlegm, blood stasis, stones, etc.

Etiology includes both pathogenic causes and conditions, which play different roles in the occurrence of diseases. Pathogenic causes refer to various factors that can cause diseases and endow them with characteristic features. Conditions are factors that exist simultaneously with the causes and promote the occurrence and development of diseases. The theory of etiology studies pathogenic factors, their nature, characteristics, and clinical manifestations.

According to the theory of the struggle between the righteous and the evil, Traditional Chinese Medicine (TCM) believes that whether it is external pathogenic factors from the six excesses or internal injuries from the seven emotions and diet, under conditions of strong righteous qi and normal physiological function, they will not lead to disease. Only when the righteous qi is weak and the body’s functional activities cannot adapt to changes in these factors will they become pathogenic factors that cause disease.

In the process of disease occurrence and development, causes and effects are mutually restrictive and interact with each other. Under certain conditions, causes and effects can transform into each other. In a certain pathological stage, it may be the result of pathology, while in another stage, it may become the cause of disease. For example, phlegm and blood stasis are pathological products formed by the dysfunction of the organs and qi-blood, but once these pathological products are formed, they can become new causes, leading to other pathological changes and various symptoms and signs. This causal relationship between etiology and pathology occurs through the dysfunction of the body’s organs.

Regarding the classification of etiology, different classification methods have been proposed by various medical practitioners throughout the development of TCM. For instance, the Yin-Yang classification method in the “Huangdi Neijing,” and the three causes classification method by Zhang Zhongjing in the Han Dynasty and Chen Wuzhe in the Song Dynasty. The Yin-Yang etiology theory categorizes external pathogenic factors such as wind, rain, cold, heat, and humidity as Yang, while internal factors such as diet and emotions are categorized as Yin. Zhang Zhongjing summarized the causes of diseases into three pathways based on transmission, categorizing those caused by evil affecting the meridians and organs as internal causes, while superficial diseases are categorized as external causes. Chen Wuzhe combined the causes with the pathways of disease onset, clearly proposing the three causes theory, categorizing the six excesses as external causes, the seven emotions as internal causes, and diet, overwork, and animal bites as neither internal nor external causes. The three causes theory proposed by Chen Wuzhe in the “San Yin Ji Yi Bing Zheng Fang Lun” is relatively systematic and clear in its classification of etiology, significantly influencing later generations of practitioners. The ancient method of combining pathogenic factors with pathways of disease onset has certain guiding significance for clinical differentiation.

This chapter classifies etiology into four categories based on the pathways and formation processes of diseases: external pathogenic factors, internal injuries, causes of pathological product formation, and other causes.

Characteristics of TCM etiology:

1. Holistic view: TCM believes that the internal organs and tissues of the human body, as well as the relationship between the body and the external environment, form a unified whole. Therefore, TCM connects the functions of the human body with the natural environment, exploring the role of pathogenic factors in the occurrence, development, and changes of diseases from a holistic, interconnected, and developmental perspective. Guided by the holistic view of the unity of heaven and man, TCM dialectically explores the roles of climate changes, diet, overwork, and emotional activities in the disease process, laying the theoretical foundation for TCM etiology. For example, the liver corresponds to wood, which is associated with spring, the six qi corresponds to wind, the five tastes correspond to sour, and the emotion corresponds to anger, while the liver is associated with tendons and opens to the eyes, corresponding to the gallbladder. Therefore, abnormal climatic changes such as “wind,” excessive emotional outbursts of “anger,” and dietary imbalances of “sour” can all become causes of liver diseases. Once the liver becomes diseased, it can lead to pathological changes in the liver’s functional systems, such as the gallbladder, tendons, and eyes.

2. Differentiation and seeking causes: The occurrence of all diseases is the result of certain pathogenic factors affecting and acting on the body. Due to the different nature of the pathogenic factors and their characteristics, as well as the body’s varied responses to these factors, the symptoms and signs presented are also different. Therefore, by analyzing the clinical manifestations reflected by the disease, one can infer the etiology, providing a theoretical basis for clinical treatment. By summarizing the regularities from the body’s response state, changes in living conditions, and treatment methods, one can infer the etiology from symptoms and signs. This method is called “differentiation and seeking causes,” which is a unique method in TCM for understanding etiology. For instance, if a patient presents with migratory pain or itching all over the body, it is confirmed that the cause is “wind” due to the nature of wind being mobile. All factors that produce this clinical manifestation are summarized as “wind” evil. In clinical practice, regardless of how complex the actual pathogenic factors are, as long as the body exhibits a reaction state of “wind,” it can be generalized as “wind evil.” During treatment, as long as appropriate “wind-dispelling” medications are used, the clinical symptoms can disappear, thus eliminating the pathogenic factors and their pathological responses. Only by using the method of differentiation and seeking causes to understand etiology, linking the study of etiology with the analysis of symptoms and signs, can it provide guidance for clinical treatment.

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Section 1: External Pathogenic Factors

External pathogenic factors refer to those that enter from the outside, either through the skin and hair or through the mouth and nose, causing external diseases. External diseases are a category of diseases caused by external pathogenic factors, generally characterized by acute onset, with initial symptoms often including chills, fever, sore throat, and joint pain. External pathogenic factors can be roughly divided into two categories: the six excesses and epidemics.

1. The Six Excesses

(1) Basic concept of the six excesses

1. Six Qi and Six Excesses

(1) Six Qi: The so-called six qi, also known as the six origins, refers to the six types of normal climatic conditions: wind, cold, heat, humidity, dryness, and fire. The changes in the six qi are referred to as the six transformations. These normal climatic changes are conditions for the growth of all things and are harmless to the human body. Due to the body’s self-regulatory mechanisms during life activities, it has developed a certain adaptability, allowing physiological activities to align with the changes in the six qi. Therefore, normal six qi generally does not easily cause disease.

(2) Six Excesses: The so-called six excesses are a collective term for the six external pathogenic evils: wind, cold, heat, humidity, dryness, and fire. The shifts in Yin and Yang, the changes in cold and heat, and climatic changes all have certain rules and limits. If climatic changes are abnormal, leading to excessive or insufficient six qi, or if the qi appears out of season (for example, cold in spring when it should be warm, or heat in winter when it should be cool), or if climatic changes occur too rapidly (such as sudden cold or warmth), exceeding certain limits, causing the body to be unable to adapt, it will lead to the occurrence of diseases. Thus, the six qi, which are harmless to the human body, transform into harmful factors, becoming pathogenic. The six qi that can lead to diseases are referred to as “six excesses.” While climatic changes are closely related to the occurrence of diseases, abnormal climatic changes do not cause disease in everyone. Some individuals can adapt to these abnormal changes without falling ill, while others cannot adapt and become ill. The same abnormal climatic change can be considered a six excess for the former group. Conversely, when climatic changes are normal, even in favorable conditions, some individuals with low adaptability may still become ill. This shows that the six excesses exist objectively in both abnormal and normal climatic conditions. The decisive factor here is the differences in people’s constitutions and the strength of their righteous qi. Only when the righteous qi is insufficient and resistance decreases can the six qi become pathogenic factors, invading the body and causing disease. In this sense, the six excesses are a category of pathogenic factors that can cause external diseases due to changes in the six qi that disrupt the body’s relative dynamic balance. The six excesses are also known as “six evils.”

2. External Six Excesses and Internal Five Evils

External six excesses are pathogenic factors of external diseases, referred to as external evils, while internal five evils refer to pathological changes such as internal wind, internal cold, internal humidity, internal dryness, and internal heat (fire) caused by the imbalance of Yin and Yang, qi, and blood in the organs, which falls under the category of pathogenesis. Although the clinical manifestations of internal five evils are similar to the pathogenic characteristics and pathological responses of the six excesses, they are distinguished from the external evils of wind, cold, humidity, dryness, and heat by the prefix “internal,” hence referred to as “internal five evils.” The clinical manifestations of internal five evils generally do not exhibit exterior symptoms, mostly presenting as either deficiency or excess syndromes, or a mixture of both. After the external six excesses act on the body, they cause dysfunction of the Yin and Yang, qi, and blood of the organs, leading to pathological changes, which often present with exterior symptoms and are mostly excess syndromes. Pure summer heat evil generally does not present with exterior symptoms, but when combined with humidity, it is referred to as summer heat and can present with exterior symptoms. Only when the external evil directly invades can interior symptoms be observed.

External six excesses and internal five evils are distinct as pathogenic factors and pathological results, yet they are closely related. When the six excesses harm the body, they can invade the interior and damage the organs, easily leading to the harm of internal five evils. Conversely, when internal five evils arise from dysfunction of the organs, they can easily be affected by the six excesses.

(2) General characteristics of diseases caused by the six excesses

1. Seasonality and regionality

(1) The relationship between diseases caused by the six excesses and seasons: Since the six excesses are primarily the excessive or insufficient manifestations of the seasonal qi, they are prone to seasonal outbreaks. For example, wind diseases are more common in spring, heat diseases in summer, humidity diseases in late summer and early autumn, dryness diseases in late autumn, and cold diseases in winter. This is a general rule. However, climatic changes are complex, and different constitutions have different sensitivities to external evils, so different types of external diseases can occur in the same season.

(2) The relationship between diseases caused by the six excesses and the environment: Working or living in unsuitable environments can also lead to the invasion of the six excesses and cause diseases. For instance, prolonged exposure to damp environments often leads to diseases caused by humidity, while working in high-temperature environments frequently results in heat, dryness, or fire evils. Dry environments are often associated with dryness evils.

2. Singularity and compatibility: The six excesses can cause diseases both individually and in combination. For instance, cold evil can directly invade the organs and cause diarrhea, while two or more evils can simultaneously invade the body and cause diseases, such as wind-cold colds, damp-heat diarrhea, and wind-cold damp bi.

3. Transformability: After the six excesses cause diseases, during the development of the disease, they can not only influence each other but also transform into different pathological natures under certain conditions. For example, cold evil can become heat due to stagnation, prolonged summer heat can transform into dryness and injure Yin, and all six excesses can transform into fire. This transformation is related to the constitution of the individual; some individuals are more prone to transformation due to their constitution. Generally, when the evil qi first invades, it is not easily transformed, but when it stagnates for a long time, it is more likely to transform.

4. External nature: The six excesses often have a process of transmission from the exterior to the interior. The evils of the six excesses typically enter through the skin or mouth and nose, invading the body and causing diseases. In the initial stage of disease caused by the six excesses, the main clinical features are chills, fever, thin white tongue coating, and floating pulse, referred to as exterior symptoms. If exterior symptoms are not eliminated, the disease can progress from the exterior to the interior, from superficial to deep. Therefore, diseases caused by the six excesses often have a process of transmission from the exterior to the interior. Even if they directly invade the interior without exterior symptoms, they are still referred to as “external diseases.” Thus, the six excesses are considered the causes of external diseases.

The nature and pathogenic characteristics of the six excesses in TCM etiology are derived from observations of natural phenomena, abstracted and generalized. The diseases caused by the six excesses, in addition to climatic factors, also include various pathogenic factors such as biological (bacteria, viruses, etc.), physical, and chemical factors that act on the body and cause pathological reactions.

(3) The nature and pathogenic characteristics of the six excesses

1. Wind

(1) Natural characteristics: Wind has the characteristics of lightness, dispersion, and movement, being the main qi of spring. Among the twenty-four solar terms, the four terms of Major Cold, Beginning of Spring, Rain Water, and Waking of Insects are dominated by wind qi. Since wind is associated with wood qi and corresponds to the liver, spring is referred to as the season of wind and wood. Although wind is the main qi of spring, it is present throughout the year and in all seasons. Therefore, diseases caused by wind are more common in spring but can occur in other seasons as well.

(2) The nature and pathogenic characteristics of wind evil: Wind is characterized by lightness, mobility, and variability, and is considered the leader of all diseases.

① Lightness and dispersion: Wind is a Yang evil, characterized by lightness, dispersion, and upward movement. Therefore, when wind evil causes disease, it tends to harm the upper body, easily affecting the skin, muscles, and other Yang locations. If the lung is affected, it can lead to symptoms such as nasal congestion, runny nose, throat itching, and coughing. If wind disturbs the head and face, symptoms such as dizziness, headaches, neck stiffness, and facial paralysis may occur. If wind evil affects the skin, symptoms such as aversion to wind and fever may be observed. Due to its dispersive nature, wind evil can invade the skin, causing the pores to open, leading to sweating and aversion to wind.

② Mobility and variability: Wind is characterized by its ability to move and change unpredictably. This means that diseases caused by wind can have migratory symptoms and can occur in various locations. For example, wind rash and urticaria can appear in different locations, and migratory joint pain (wind bi) is a manifestation of excessive wind qi. The variability of wind also means that diseases can appear suddenly and change rapidly, such as in cases of wind rash, urticaria, sudden fainting, or stroke. In summary, diseases led by wind evil, whether external or internal, generally exhibit characteristics of rapid onset, frequent changes, and quick transmission.

③ Proactive nature of wind: The proactive nature of wind means that diseases caused by wind tend to be unstable. This is often manifested by symptoms such as dizziness, tremors, limb spasms, and convulsions, hence the saying “when wind prevails, movement occurs.” For example, in external heat diseases, “extreme heat generates wind,” and in internal mixed diseases, “liver Yang transforms into wind” or “blood deficiency generates wind” are all manifestations of wind evil’s instability.

④ Wind as the leader of all diseases: Wind evil is the precursor of external pathogenic factors, and cold, humidity, dryness, and heat evils often attach themselves to wind to invade the body. For instance, when combined with cold, it becomes wind-cold evil; with heat, it becomes wind-heat evil; with humidity, it becomes wind-damp evil; with summer heat, it becomes summer wind; with dryness, it becomes wind-dryness; and with fire, it becomes wind-fire. Therefore, clinically, wind evil is frequently encountered and easily combines with other evils to cause diseases, hence it is referred to as the leader of all diseases and the first among the six excesses.

Wind corresponds to the liver. Wind is wood qi, which connects to the liver. External wind evil can lead to symptoms such as stomach pain, abdominal distension, bowel sounds, vomiting, and diarrhea, which are caused by wind evil harming the liver, as wood excessively restrains earth.

In summary, wind is the main qi of spring and corresponds to the liver wood. Wind evil causes diseases that are widespread and change rapidly. Its specific characteristics include: ① affecting the entire body: it can invade any part of the body, from the head to the feet, externally affecting the skin and internally affecting the organs. ② Mediating role: it can combine with cold, humidity, heat, dryness, and fire to cause diseases. ③ Its pathogenic nature: wind diseases have rapid onset and short duration, and their specific symptoms are easy to recognize, such as sweating, aversion to wind, itching, migratory symptoms, and instability. In clinical practice, if the onset occurs in spring and is clearly related to wind evil, the presence of wind evil should be considered.

2. Cold

(1) Natural characteristics: Cold has the characteristics of coldness and condensation, being the main qi of winter. The four solar terms of Minor Snow, Major Snow, Winter Solstice, and Minor Cold are dominated by cold qi. Cold is associated with water qi and corresponds to the kidney, hence winter is referred to as the season of cold water. Since winter is the season of cold qi, cold diseases are more common in winter but can also occur in other seasons. Due to sudden drops in temperature and insufficient protection against the cold, the body is also prone to cold evil.

(2) The nature and pathogenic characteristics of cold evil: Cold evil is characterized by coldness, stagnation, and contraction.

① Cold easily harms Yang: Cold is a manifestation of Yin qi, and its nature belongs to Yin. Cold is a Yin evil. Yang qi can normally control Yin, but when Yin cold predominates, Yang qi is not only insufficient to expel cold evil but is also harmed by Yin cold, hence the saying “when Yin prevails, cold prevails” and “when Yin prevails, Yang becomes ill.” Therefore, cold evil is most likely to damage the body’s Yang qi. When Yang qi is damaged, it loses its warming function, leading to obvious cold symptoms in the whole body or locally. For instance, if cold evil binds the exterior, it can cause symptoms such as aversion to cold, fever, and no sweating, referred to as “cold damage.” If cold evil directly invades the interior and harms the Yang qi of the organs, it is referred to as “internal cold.” For example, if it harms the spleen and stomach, it can lead to abnormal digestion, resulting in vomiting and diarrhea; if it affects the lungs and spleen, it can lead to cough and shortness of breath, with clear phlegm or edema; if it harms the spleen and kidney, it can lead to cold limbs, lower back pain, clear urination, loose stools, and abdominal edema; if it affects the heart and kidney Yang, it can lead to symptoms such as aversion to cold, curled up posture, cold hands and feet, clear diarrhea, mental fatigue, and a weak pulse.

② Cold nature of stagnation: Stagnation refers to the obstruction and blockage. The movement of qi, blood, and body fluids in the human body relies on the warming effect of Yang qi to flow smoothly. When cold evil invades the body, the meridians and blood lose the warming effect of Yang qi, easily leading to stagnation and blockage of qi and blood, resulting in pain. Pain caused by cold is alleviated by warmth and worsens with cold; warmth allows qi to rise and blood to disperse, leading to unobstructed movement of qi and blood, thus alleviating or reducing pain. Cold predominates, leading to pain, but pain does not necessarily mean cold. Due to the different locations affected by cold evil, the symptoms vary. If cold affects the skin, it can cause severe pain in the head, body, and limbs; if cold evil directly invades the interior, it can cause cold pain or cramping in the chest, abdomen, or intestines.

③ Cold nature of contraction: Contraction refers to the pulling and tightening nature. The cold nature of contraction means that cold evil has the characteristic of constriction and tightness. When cold evil invades the body, it can cause the qi mechanism to contract, the pores to close, and the meridians and tendons to tighten; if cold affects the joints, it can lead to tightness and pain, resulting in difficulty in bending and stretching or numbness; if cold evil invades the skin, it can cause the pores to contract, leading to aversion to cold and no sweating.

Cold corresponds to the kidney. Cold is water qi, which connects to the kidney. When cold evil invades, excessive cold water can lead to reduced urination and edema; excessive cold water can also suppress heart fire, leading to heart pain, palpitations, and cold extremities.

In summary, cold is the main qi of winter and corresponds to kidney water. Cold diseases are more common in winter but can also occur in other seasons. The pathogenic characteristics of cold evil include: cold as a Yin evil, easily harming Yang qi, leading to obvious cold symptoms in the whole body or locally. Cold predominates, leading to pain, making pain an important characteristic of cold syndrome. Due to cold, the qi contracts, leading to symptoms such as closed pores, contracted qi, and tightness in the tendons, manifesting as no sweating, tightness, and pain or difficulty in bending and stretching.

3. Heat

(1) Natural characteristics: Heat is a fire evil, being the main qi of summer. The four solar terms of Minor Fullness, Grain in Ear, Summer Solstice, and Minor Heat are dominated by heat qi. Heat evil has obvious seasonality, primarily occurring between the summer solstice and the beginning of autumn. Heat evil is unique to summer, hence the saying “heat is an external evil, and there is no internal heat.” Heat evil has both Yin and Yang aspects; during hot summer days, excessively high temperatures, prolonged exposure to the sun, or working in hot environments can lead to heat diseases, classified as Yang heat; while during hot weather, excessive consumption of cold foods, sleeping in the open, or prolonged cold baths can lead to heat diseases classified as Yin heat. In summary, heat in summer can be classified as Yin heat or Yang heat.

(2) The nature and pathogenic characteristics of heat evil: Heat is transformed from fire, primarily characterized by upward movement and often accompanied by humidity.

① Heat is characterized by its fiery nature: Heat is the fire of summer, possessing extreme heat, and being Yang in nature, hence heat is classified as a Yang evil. Heat evil often manifests with a series of Yang heat symptoms, such as high fever, irritability, flushed face, restlessness, and a rapid pulse, referred to as heat damage (or summer heat).

② Heat is characterized by upward movement: Upward movement refers to the tendency of heat evil to rise and disperse. Heat evil easily invades the head and disturbs the heart, as it tends to enter the heart. It also tends to harm the body fluids and qi. As a Yang evil, heat has an upward dispersive nature, so when heat evil invades the body, it often directly enters the qi level, causing the pores to open and leading to excessive sweating. Excessive sweating can damage body fluids, leading to symptoms such as thirst, dry lips, and scanty, dark urine. During excessive sweating, qi can also be lost, leading to qi deficiency, hence those harmed by heat often exhibit symptoms of shortness of breath and fatigue, and in severe cases, sudden fainting and loss of consciousness, known as heat stroke. Heat stroke can also present with cold extremities, referred to as heat syncope. Heat can also provoke liver wind, leading to symptoms such as limb spasms, stiff neck, and even convulsions, referred to as heat wind (heat epilepsy). Heat evil not only consumes qi and damages body fluids but can also disturb the heart and lead to irritability and restlessness.

③ Heat often accompanies humidity: The summer season is not only hot but also often rainy and humid, leading to a combination of heat and humidity. The clinical characteristics of heat evil include not only fever and thirst but also symptoms of heaviness, chest tightness, nausea, and loose stools due to damp obstruction. Although heat and humidity coexist, heat is the primary concern, while dampness is secondary; it is not necessary for heat to always be accompanied by dampness. Heat is the main qi of summer, and heat evil can be classified into Yin heat and Yang heat. The basic characteristics of heat evil include excessive heat, Yin damage, qi consumption, and often accompanied by dampness. Therefore, clinically, heat evil is characterized by strong heat, Yin deficiency, qi deficiency, and damp obstruction.

4. Humidity

(1) Natural characteristics: Humidity has the characteristics of heaviness, stickiness, and downward tendency, being the main qi of late summer. The four solar terms of Major Heat, Beginning of Autumn, End of Heat, and White Dew are dominated by humidity qi. Humidity corresponds to the spleen earth. During the transition from summer to autumn, humidity is at its peak, leading to many humidity-related diseases. Humidity can also arise from exposure to water, rain, or living in damp conditions. Humidity can cause diseases in all seasons, and its harm is often slow and difficult to detect.

(2) The nature and pathogenic characteristics of humidity: Humidity is a Yin evil that obstructs the qi mechanism and easily harms Yang qi, characterized by heaviness, stickiness, and a downward tendency.

① Humidity is a Yin evil that obstructs the qi mechanism and damages Yang qi: Humidity is similar to water, which belongs to Yin, hence humidity is classified as a Yin evil. When humidity invades the body, it tends to stagnate in the organs and meridians, obstructing the qi mechanism and leading to abnormal movement of qi. For instance, if humidity obstructs the chest, it can lead to chest tightness; if it obstructs the spleen and stomach, it can lead to symptoms such as loss of appetite, abdominal distension, and loose stools. Since humidity is a Yin evil, when Yin predominates, it can lead to Yang diseases. The spleen governs the transformation and transportation of water and dampness, and being an earth element, it is particularly sensitive to humidity. Therefore, when humidity invades the body, it tends to affect the spleen, leading to spleen Yang deficiency, stagnation of water and dampness, resulting in diarrhea, edema, and reduced urination. “When humidity prevails, Yang is weak,” as humidity is a Yin evil that easily harms Yang qi, leading to stagnation and obstruction of Yang qi, which can be resolved through methods that transform qi and drain dampness.

② Humidity is characterized by heaviness and stickiness: Humidity is a heavy and turbid evil. The term “heavy” refers to the quality of being heavy and burdensome. Therefore, diseases caused by humidity often present with heavy symptoms, such as heaviness in the head and body, and aching limbs. If humidity invades the skin, it can lead to symptoms such as dizziness and heaviness, as if being bound; if it stagnates in the joints, it can lead to numbness and pain. The term “turbid” refers to the quality of being dirty and unclean. Therefore, when humidity invades, it can lead to symptoms of unclean secretions and excretions. For instance, if humidity is present in the upper body, it can lead to facial blemishes and excessive eye discharge; if it stagnates in the large intestine, it can lead to loose stools, dysentery with pus and blood, and if it descends, it can lead to cloudy urine and excessive vaginal discharge; if humidity invades the skin, it can lead to sores, eczema, and purulent infections.

③ Humidity is characterized by stickiness: Stickiness refers to the quality of being sticky and stagnant. This characteristic is mainly reflected in two aspects: one is the stickiness of symptoms, meaning that symptoms of humidity are often sticky and uncomfortable, such as sticky stools, difficult urination, and sticky secretions. The second aspect is the chronic nature of the disease. Due to the sticky nature of humidity, it is difficult to resolve, leading to slow onset and prolonged duration, often resulting in recurrent or lingering conditions. For example, damp-heat is an external heat disease caused by damp-heat evil. Due to the specific nature of humidity, during the transmission of the disease, it often presents with slow onset, slow transmission, long duration, and difficulty in rapid recovery, such as eczema and damp bi (obstruction due to dampness).

④ Humidity tends to descend: Water tends to flow downward, and humidity is similar to water, hence humidity has a downward tendency, easily affecting the lower parts of the body. Symptoms of diseases caused by humidity are often observed in the lower body, such as edema, excessive vaginal discharge, diarrhea, and dysentery, which are often caused by humidity descending. However, humidity can invade both the upper and lower parts of the body, affecting the body internally and externally. The saying “those harmed by humidity are first affected below” in the “Suwen: Taiyin Yangming Lun” indicates that humidity tends to descend, easily invading the Yin locations, which is one of its characteristics.

Humidity corresponds to the spleen earth. Humidity has the nature of obstructing the qi mechanism and easily harming Yang qi, characterized by heaviness, stickiness, and a downward tendency. Therefore, diseases caused by humidity manifest as obstruction of the body’s qi mechanism, spleen Yang deficiency, and stagnation of water and dampness, leading to symptoms such as chest tightness, abdominal distension, heaviness in the limbs, nausea, and diarrhea, as well as unclean secretions and excretions such as tears, nasal discharge, phlegm, vaginal discharge, and urine.

5. Dryness

(1) Natural characteristics: Dryness has the characteristics of being dry, constricting, and clearing, being the main qi of autumn. The four solar terms of Autumn Equinox, Cold Dew, Frost’s Descent, and Beginning of Winter are dominated by dryness qi. During autumn, the weather is clear and dry, with a lack of moisture, leading to many dryness-related diseases. Dryness qi is transformed from the dry heat of autumn and is classified as a Yang evil among the Yin.

(2) The nature and pathogenic characteristics of dryness: Excessive dryness leads to dryness and is likely to harm the lungs, which is the basic characteristic of dryness evil.

① Dryness harms body fluids: Dryness is the qi of autumn, characterized by dryness and depletion. Dryness evil is most likely to consume the body’s fluids, leading to various symptoms and signs of dryness, such as dry and cracked skin, dry nose and throat, cracked lips, dry and brittle hair, scanty urination, and dry stools.

② Dryness easily harms the lungs: The lungs are the “canopy” of the five organs and are sensitive to dryness, as they prefer moist and dislike dryness. Dryness evil often enters through the mouth and nose. Dryness corresponds to the main qi of autumn and is associated with the lungs, hence dryness evil is most likely to harm the lungs. When dryness evil invades the lungs, it can damage lung fluids, leading to symptoms such as dry cough with little phlegm, or phlegm that is difficult to expectorate, or blood-streaked phlegm, as well as wheezing and chest pain.

In summary, dryness is the main qi of autumn and corresponds to the lungs. Dryness evil is characterized by harming body fluids and easily harming the lungs. Whether external or internal dryness, symptoms of dryness in the mouth, nose, throat, and lips, as well as dry skin and hair, can be observed.

6. Fire (Heat)

(1) Natural characteristics: Fire has the characteristics of heat and is predominant in summer. The four solar terms of Spring Equinox, Clear and Bright, Grain Rain, and Beginning of Summer are dominated by fire qi. Since summer is the season of fire, fire corresponds to the heart qi. However, fire does not have the same obvious seasonality as heat and is not limited by seasonal climate.

(2) The relationship between warmth, heat, fire, and heat: Warmth, heat, fire, and heat have similar basic properties but also differences.

Warmth and heat: Here, warmth and heat refer to pathogenic evils. Warmth is the mild form of heat, while heat is the extreme form of warmth; the two differ only in degree, with no essential difference, hence they are often referred to together. In the study of warm diseases, the term warm evil refers to all warm and hot pathogenic evils, without regard to differences in degree.

Heat and fire: Heat is the main qi of summer and is transformed from fire, hence heat is a fire evil. However, heat is unique to summer and is purely an external evil, with no internal heat. Fire (heat) as a disease does not have obvious seasonality and also includes high temperatures and heat from burning.

Fire and heat: Fire is the source of heat, while heat is the nature of fire. Fire and heat are both manifestations of excessive Yang, hence they are often referred to together. However, there are still certain differences; heat is purely an evil qi and does not refer to righteous qi. Fire, on the other hand, refers to the body’s righteous qi, known as “less fire,” and also refers to pathogenic evil, known as “excess fire.” This is the main distinction between fire and heat. Generally speaking, heat is more often associated with external factors, such as wind-heat, summer heat, and warm heat. Fire, however, often arises from internal factors, primarily due to imbalances in the Yin and Yang, qi, and blood of the organs, such as heart fire rising, liver fire blazing, and gallbladder fire reversing.

In terms of warmth, heat, and fire, although they are all one qi, warmth can transform into heat, and heat can generate fire, indicating a certain degree of difference. Warmth is the mild form of heat, heat is the extreme form of warmth; heat is the gradual form of fire, while fire is the extreme form of heat.

(3) The meaning of fire: In TCM, fire can be divided into physiological and pathological, internal and external fire.

① Physiological fire: Physiological fire is a type of Yang qi necessary for maintaining normal life activities, hidden within the organs, and has warming and transformative effects. This beneficial Yang qi is referred to as “less fire,” which belongs to the category of righteous qi.

② Pathological fire: Pathological fire refers to excessive Yang, which consumes the body’s righteous qi. This type of fire is referred to as “excess fire.” Pathological fire can also be divided into internal and external fire.

External fire: External fire can arise from exposure to warm and hot evils, or from the transformation of external evils such as wind, cold, heat, humidity, and dryness into fire, known as “five qi transforming into fire.” Among the five evils, only summer heat is purely an external fire, referred to as summer heat. The other evils, such as wind, cold, humidity, and dryness, are not fire evils, but they can transform into fire under certain conditions. First, they must be obstructed to transform into fire. For instance, cold can transform into heat, extreme heat can generate fire, warmth and heat can combine, or dampness can transform into heat, leading to extreme heat. Fire can also arise from dryness. Second, the transformation of fire varies among individuals; those with excessive Yang or deficient Yin are more prone to transformation. Third, the location of the evil invasion also matters. For example, if the evil invades the Yangming dry earth, it is more likely to transform into fire; if cold evil directly invades the spleen, it can also transform into fire. Additionally, the ability of the five evils to transform into fire is related to treatment. Internal fire: Internal fire often arises from dysfunction of the organs, leading to imbalances in Yin and Yang, qi, and blood. Extreme emotional states can also lead to internal fire, known as “five emotions transforming into fire.”

In TCM, fire is classified into righteous and evil categories. Righteous fire refers to less fire, which can be further divided into “sovereign fire” and “ministerial fire.” “Sovereign fire” refers to the Yang qi of the heart, while “ministerial fire” refers to the Yang qi of the liver, kidney, gallbladder, bladder, pericardium, and sanjiao. Among these, the Yang qi of the kidney is also known as “mingmen fire” or “dragon fire,” while the Yang qi of the liver is referred to as “thunder fire.” “Sovereign fire” refers only to righteous qi; if it becomes excessive, it is termed “heart fire blazing.” “Ministerial fire” encompasses both righteous and evil aspects; when excessive, it is termed “ministerial fire in chaos.” Both “heart fire blazing” and “ministerial fire in chaos” belong to “excess fire,” which is classified as evil qi.

(4) The nature and pathogenic characteristics of fire evil: Fire evil is characterized by burning, upward movement, consumption of qi, damage to body fluids, and stirring of blood.

① Fire is characterized by burning: Burning refers to the act of combustion; scorching refers to the act of burning. Fire evil has the characteristic of burning and scorching. Therefore, when fire evil causes disease, the primary pathological mechanism is excessive Yang qi, clinically manifesting as high fever, aversion to heat, and a rapid pulse, which are characteristic of heat.

② Fire is characterized by upward movement: Fire is a Yang evil, and its nature is to rise. Therefore, fire evil tends to manifest in the upper body. For instance, if heart fire rises, it can lead to symptoms such as a red and painful tongue, oral ulcers, and sores; if liver fire rises, it can lead to symptoms such as severe headaches and red, swollen eyes; if stomach fire is excessive, it can lead to swollen gums and bleeding gums.

③ Fire consumes body fluids and qi: Fire evil, when it invades the body, tends to consume body fluids, leading to symptoms such as thirst, dry mouth, scanty and dark urine, and constipation. Excessive fire can also lead to a decline in the body’s physiological functions, resulting in systemic symptoms of fatigue and weakness. In summary, fire evil can either directly harm the body’s righteous qi or lead to qi deficiency due to the consumption of body fluids, ultimately resulting in a pathological outcome of both body fluid deficiency and qi consumption.

④ Fire can stir wind and blood: Fire evil can easily lead to internal wind and erratic blood flow.

Stirring wind: When fire evil invades the body, it often burns the liver meridian, consuming body fluids and blood, leading to internal wind. This is referred to as “extreme heat generating wind.” The combination of wind and fire can lead to rapid symptoms, clinically manifesting as high fever, confusion, limb spasms, stiff neck, and even convulsions.

Stirring blood: Blood coagulates in cold and flows in heat. Fire evil, when it invades the body, can lead to rapid blood flow, causing various bleeding symptoms such as hemoptysis, epistaxis, hematochezia, hematuria, and skin rashes, as well as excessive menstruation and uterine bleeding. Fire evil can also lead to the formation of sores and abscesses, as fire can lead to the accumulation of toxins in the blood, resulting in localized redness, swelling, and pain.

In summary, fire can be classified into physiological and pathological fire. The fire discussed in this section is pathological fire, also known as fire evil. Fire evil can arise from external sources or internal sources. External fire often arises from external factors, while internal fire often arises from internal dysfunction. Fire evil is characterized by burning, upward movement, consumption of qi, damage to body fluids, stirring of blood, and can easily lead to sores and disturbances of the mind. Its pathogenic effects are widespread, with rapid onset and can spread rapidly. Clinically, it presents with high fever, body fluid deficiency, qi deficiency, internal wind, bleeding, and abnormal mental states.

2. Epidemic Qi

(1) Basic concept of epidemic qi

Epidemic qi is a type of highly infectious pathogenic evil, also known as pestilential qi, epidemic evil, toxic qi, foreign qi, mixed qi, and perverse qi. Epidemic qi is transmitted through the air and contact. Epidemic qi differs from the six excesses in that it is not a pathogenic factor formed by climatic changes but rather a small substance (pathogenic microorganisms) that cannot be directly observed by human senses, referred to as “toxic” evil. Epidemic qi enters the body through the mouth and nose, hence it is classified as an external pathogenic factor. Diseases caused by epidemic qi, which are characterized by severe infectious outbreaks, are referred to as epidemics, pestilences, and plagues. Warm diseases differ from epidemics; warm diseases are a general term for various acute febrile diseases caused by external factors, which are not infectious or epidemic.

(2) The nature and pathogenic characteristics of epidemic qi

1. Rapid onset and severe illness: Epidemic qi is characterized by rapid onset, burning heat, and intense toxicity. Therefore, its pathogenic effects are characterized by rapid onset, fierce momentum, severe illness, variable changes, and quick transmission, and it can easily harm body fluids, disturb the mind, stir blood, and generate wind. The harm caused by epidemic qi is similar to that of fire heat, presenting a picture of excessive heat, but the toxicity of epidemic qi is often more severe than that of fire heat, as it not only has intense heat and toxicity but often carries damp toxins, toxic mists, and pestilential qi, making its pathogenic effects more severe and deadly.

2. Strong infectivity and tendency to spread: Epidemic qi has strong infectivity and can spread through various routes among people, including through the mouth and nose. Epidemic qi can cause sporadic outbreaks or large-scale epidemics. Therefore, epidemic qi is characterized by strong infectivity, widespread outbreaks, and high mortality rates. Examples include diseases such as mumps (characterized by swelling of the head and face or sore throat), toad plague (characterized by swelling of the neck and head), epidemic dysentery, diphtheria, scarlet fever, smallpox, cholera, and plague, which include many infectious diseases and severe infectious diseases recognized by modern medicine.

3. Specificity and partiality: Specificity refers to the specific location and type of disease caused by epidemic qi. The effects of epidemic qi on different organs and the diseases they cause have specific localization characteristics. Epidemic qi has a certain selectivity in its effects on the body, leading to corresponding symptoms in different locations. Different types of epidemic qi cause different diseases, each with its own clinical characteristics and transmission patterns, referred to as “one qi causes one disease.” Partiality refers to the susceptibility of epidemic qi to humans or animals. Epidemic qi can be specific to humans or animals, meaning that it does not transmit between species. Even if it is specific to animals, due to the differences in species, it does not transmit between them.

In summary, both the six excesses and epidemic qi are classified as external pathogenic evils, with different natures and pathogenic characteristics. However, the diseases they cause are often characterized by heat, hence they are commonly referred to as external febrile diseases.

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Section 2: Internal Injury Etiology

Internal injury etiology, also known as internal injury, refers to pathogenic factors that arise from emotional disturbances or behaviors that exceed the body’s self-regulatory capacity, directly harming the organs and causing disease, such as internal injuries from the seven emotions, improper diet, and imbalances in work and rest. Internal injury etiology leads to imbalances in the qi, blood, Yin, and Yang of the organs, resulting in disease. Diseases caused by internal injury etiology are referred to as internal injury diseases. Internal injury etiology is contrasted with external pathogenic factors, as the disease arises from within rather than from external evils.

1. The Seven Emotions

(1) Basic concept of the seven emotions

The seven emotions refer to the normal emotional activities of joy, anger, worry, thought, sadness, fear, and shock, which are responses of human consciousness to external events. The seven emotions are closely related to the functional activities of the organs. The seven emotions are categorized according to the five organs, with joy, anger, thought, sadness, and fear representing the five emotions.

The seven emotions are different responses to objective events, and within normal limits, they generally do not cause disease. Only when emotional stimuli are sudden, intense, or prolonged, exceeding the normal physiological range of the body, can they disrupt the qi mechanism and lead to imbalances in the organs’ Yin, Yang, qi, and blood, resulting in disease. Therefore, as a pathogenic factor, the seven emotions refer to excessively intense, prolonged, or sudden emotional changes that lead to imbalances in the organs’ qi, blood, Yin, and Yang. Diseases caused by the seven emotions are referred to as diseases caused by stagnation. Additionally, certain chronic diseases can lead to long-term dysfunction of the organs, resulting in abnormal emotional states, referred to as diseases causing stagnation. The seven emotions are also related to the body’s own tolerance and regulatory capacity. The pathogenic effects of the seven emotions differ from those of the six excesses, as the six excesses primarily invade the body through the mouth, nose, or skin, while the seven emotions directly affect the relevant organs and cause disease. The seven emotions can not only lead to the occurrence of various diseases but also significantly influence the progression of diseases, promoting improvement or deterioration. As one of the main pathogenic factors of internal injury diseases, the seven emotions are also referred to as “internal injury from the seven emotions.”

(2) The relationship between the seven emotions and the organs’ qi and blood

1. The relationship between the seven emotions and the organs: The emotional activities of the human body are closely related to the organs. The basic principle is: the heart governs joy, excessive joy harms the heart; the liver governs anger, excessive anger harms the liver; the spleen governs thought, excessive thought harms the spleen; the lungs govern sadness and worry, excessive sadness and worry harm the lungs; the kidneys govern shock and fear, excessive shock and fear harm the kidneys. This indicates that organ diseases can lead to corresponding emotional responses, while excessive emotional responses can also harm the relevant organs. The theory that the seven emotions arise from the five organs and can harm the five organs has important guiding significance in diagnosis and treatment.

2. The relationship between the seven emotions and qi and blood: Qi and blood are the two fundamental substances that constitute the body and maintain life activities. Qi has a warming and promoting effect on the organs, while blood nourishes the organs. Qi and blood are the material basis for the emotional activities of the body, and changes in the organs’ qi and blood can also affect emotional changes. Hence, it is said: “When blood is abundant, there is anger; when blood is deficient, there is fear.” The physiological activities of the organs must be based on qi and blood, while emotional activities are manifestations of the physiological functions of the organs, indicating a close relationship between emotional activities and the organs’ qi and blood.

(3) Pathogenic characteristics of the seven emotions

1. Related to mental stimuli: The seven emotions are considered mental pathogenic factors, and their onset is always related to significant mental stimuli. Throughout the course of the disease, changes in emotions can lead to significant changes in the condition. For example, epilepsy is often caused by emotional disturbances, while excessive worry can harm the liver, leading to liver qi stagnation, which in turn harms the spleen, resulting in phlegm and internal disturbances, leading to confusion and loss of control. Mania is often caused by excessive anger and sadness, which can harm the liver and gallbladder, leading to stagnation and transformation into fire, consuming body fluids and resulting in phlegm-fire, which disturbs the mind and leads to confusion. This illustrates the significant role of mental factors in the occurrence and progression of diseases.

2. Directly harming the organs: Excessive emotions can affect the activities of the organs and lead to pathological changes. Different emotional stimuli can harm different organs, resulting in various pathological changes. For instance, excessive joy harms the heart, leading to symptoms such as palpitations, scattered thoughts, and inability to concentrate, and in severe cases, mental disorders. Although excessive emotions can harm all five organs, the relationship with the heart and liver is particularly close. The heart is the master of all organs, and all life activities are concentrated in the functions of the five organs, which must be governed by the heart. Damage to the heart can also affect other organs. Liver dysfunction can lead to qi stagnation, which is a key mechanism in emotional diseases.

The heart governs blood and houses the spirit; the liver stores blood and governs the smooth flow of qi; the spleen governs transformation and is the pivot for the rise and fall of qi, as well as the source of qi and blood generation. Therefore, emotional injuries often manifest as imbalances in the heart, liver, and spleen, leading to qi and blood disharmony. For example, excessive joy can harm the heart, leading to anxiety, palpitations, insomnia, restlessness, and even mental disorders, such as erratic behavior and excessive talking. Unresolved anger can harm the liver, affecting its ability to regulate qi, leading to symptoms such as rib pain, irritability, and sighing, or a sensation of obstruction in the throat, or menstrual irregularities in women due to qi stagnation and blood stasis. Additionally, excessive anger can lead to liver qi rising, harming the blood vessels, resulting in severe vomiting of blood or fainting. Excessive worry can harm the spleen, leading to symptoms such as loss of appetite and abdominal distension. Emotional injuries can occur independently or interactively, leading to various complications, such as excessive worry harming the heart and spleen, or unresolved anger leading to liver-spleen disharmony.

Furthermore, excessive emotional fluctuations can lead to changes in the disease condition, such as in patients with dizziness due to Yin deficiency and Yang excess; if they encounter anger, it can lead to a sudden increase in liver Yang, causing dizziness and even fainting or stroke.

In summary, the seven emotions of joy, anger, worry, thought, sadness, fear, and shock are closely related to the internal organs. Emotional activities must be based on the essence of the five organs, and various mental stimuli can only reflect emotional changes through the functions of the relevant organs. Hence, it is said: “Humans have five organs that transform into five emotions, leading to joy, anger, sadness, worry, and fear.” Emotional disturbances primarily harm the five organs, leading to imbalances in qi, blood, and Yin and Yang, resulting in disease. The specific organs affected can vary, and while there are common patterns, one emotional change can affect multiple organs, while multiple emotions can harm a single organ. Clinical analysis should be based on specific manifestations and not treated mechanically.

2. Improper Diet

Diet is a fundamental condition for health. The essence derived from food and drink is essential for generating qi and blood, maintaining growth and development, and fulfilling various physiological functions, ensuring life and health.

Normal diet is one of the main sources for maintaining the body’s life activities, but improper diet is often a cause of many diseases. The digestive and absorption functions primarily rely on the spleen and stomach; if the diet is improper, it can first harm the spleen and stomach, leading to dysfunction in digestion and absorption, resulting in digestive disorders. Secondly, it can generate heat, phlegm, and dampness, leading to various pathological changes, becoming an important cause of disease.

Improper diet includes irregular eating patterns, unclean food, and dietary preferences. Improper diet can lead to the occurrence of diseases and is one of the main pathogenic factors of internal injury diseases.

(1) Irregular Eating Patterns

Eating should be done in moderation. Eating at fixed times and in appropriate amounts is referred to as having a regular diet.

1. Irregular hunger and satiety: Eating should be appropriate in quantity; both excessive hunger and excessive fullness can lead to disease. Eating significantly below one’s appropriate amount is referred to as excessive hunger, while eating significantly above one’s appropriate amount is referred to as excessive fullness. Excessive hunger leads to insufficient intake, resulting in a lack of resources, ultimately leading to deficiency of qi and blood. Insufficient qi and blood can lead to weight loss, weakened righteous qi, and decreased resistance, making one susceptible to other diseases. Conversely, excessive eating can exceed the digestive and absorption capacity of the spleen and stomach, leading to food stagnation, resulting in symptoms such as abdominal distension, acid reflux, loss of appetite, and vomiting or diarrhea, which harm the spleen and stomach. Hence, it is said, “Excessive eating harms the intestines and stomach.”

Irregular hunger and satiety are particularly common in children, as their spleen and stomach are weaker than those of adults. Prolonged food stagnation can lead to heat transformation; excessive consumption of cold and raw foods can lead to dampness and phlegm. In infants, prolonged food stagnation can lead to symptoms such as heat in the hands and feet, irritability, abdominal distension, and a pale, thin appearance, referred to as “accumulation disease.” In adults, prolonged overeating can obstruct the flow of qi and blood in the intestines and stomach, leading to diarrhea, hematochezia, and hemorrhoids. Excessive consumption of rich and fatty foods can easily generate internal heat, even leading to abscesses and toxic sores.

In summary, one should not eat excessively when extremely hungry, nor should one overeat; one should not drink excessively when extremely thirsty, nor should one drink too much. Excessive eating can lead to accumulation, while excessive drinking can lead to dampness and phlegm.

Additionally, during the course of a disease, irregular eating can also alter the condition, hence the saying “food recovery”; for instance, in febrile diseases, when the disease is initially resolved, if the spleen and stomach are still weak, excessive eating or consuming hard-to-digest foods can often lead to food stagnation and heat, combining with residual heat, causing the disease to recur or prolong.

Eating at irregular times: Eating at fixed times and in a regular manner can ensure that the digestive and absorption functions operate rhythmically, allowing the spleen and stomach to coordinate effectively. Since ancient times, it has been said, “Breakfast should be hearty, lunch should be filling, and dinner should be light.” If eating occurs at irregular times, it can also harm the spleen and stomach, leading to other diseases.

(2) Dietary Preferences

A reasonable dietary structure, with a balance of flavors and moderate temperatures, is essential for the body to obtain the necessary nutrients. If dietary preferences or an improper dietary structure occur, or if foods are excessively cold or hot, or if there is a preference for certain flavors, it can lead to imbalances in Yin and Yang or deficiencies in certain nutrients, resulting in disease.

1. Preference for certain types of food: A reasonable combination of food types and a balanced dietary structure are necessary to obtain sufficient nutrition to meet the needs of life activities. The dietary structure should include grains, meat, fruits, and vegetables, with grains as the main component, meat as a secondary component, vegetables as a supplement, and fruits as an aid, all in reasonable proportions. If the structure is inappropriate or the combination is unsuitable, it can lead to imbalances in flavors and organ functions, resulting in dysfunction. For example, excessive preference for fermented foods can lead to water retention; excessive preference for fruits and dairy can lead to internal dampness, resulting in swelling and diarrhea.

2. Preference for cold or hot foods: Foods should be consumed at moderate temperatures; otherwise, excessive consumption of cold and raw foods can harm the Yang qi of the spleen and stomach, leading to internal dampness and symptoms such as abdominal pain and diarrhea. Excessive consumption of spicy and warming foods can lead to heat accumulation in the stomach and intestines, resulting in symptoms such as thirst, abdominal distension, constipation, or even hemorrhoids.

3. Preference for certain flavors: The body’s qi and blood are nourished by the five flavors. Each flavor corresponds to a specific organ; for instance, sour corresponds to the liver, bitter to the heart, sweet to the spleen, spicy to the lungs, and salty to the kidneys. If one has a long-term preference for a certain type of food, it can lead to an imbalance in the functions of the corresponding organ. For instance, excessive consumption of salty foods can lead to blood stagnation and a loss of luster in the complexion; excessive consumption of bitter foods can lead to dry skin and hair loss; excessive consumption of spicy foods can lead to tightness in the tendons and brittle nails; excessive consumption of sour foods can lead to thickened skin and dry lips; excessive consumption of sweet foods can lead to bone pain and hair loss. Additionally, excessive preferences can lead to nutritional deficiencies, lacking certain essential nutrients, which can harm the organs and lead to disease. For example, beriberi, night blindness, and goiter are all results of dietary preferences. Therefore, the five flavors should be balanced, and one should avoid excessive preferences in daily diet. During illness, attention should be paid to dietary restrictions; food should be compatible with the disease, which can assist in treatment and promote recovery; conversely, inappropriate food can exacerbate the disease. Only by “carefully balancing the five flavors” can one “prolong life.”

(3) Unclean Food

Consuming unclean food can lead to various gastrointestinal diseases, resulting in symptoms such as abdominal pain, vomiting, and dysentery; it can also lead to parasitic infections, such as roundworms, pinworms, and threadworms, with clinical manifestations including abdominal pain, cravings for unusual foods, and a pale, thin appearance. If roundworms invade the bile duct, it can lead to severe upper abdominal pain, intermittent episodes, and vomiting of worms, along with cold extremities. If spoiled or toxic foods are consumed, it can lead to food poisoning, often presenting with abdominal pain and vomiting, and in severe cases, can lead to coma or death.

3. Work and Rest

Work and rest include both excessive fatigue and excessive leisure. Normal labor and physical exercise help promote the flow of qi and blood and enhance physical fitness. Necessary rest can eliminate fatigue and restore physical and mental strength, without causing illness. Only prolonged excessive fatigue, whether from physical labor, mental labor, or excessive sexual activity, or excessive leisure, with no labor or exercise, can become pathogenic factors that lead to disease.

(1) Overwork

Overwork refers to excessive fatigue, including excessive physical labor, excessive mental labor, and excessive sexual activity.

1. Excessive physical labor: Excessive physical labor primarily refers to prolonged inappropriate activities and excessive physical exertion beyond one’s capacity. Excessive physical labor can damage the functions of the internal organs, leading to deficiency of qi, resulting in symptoms such as fatigue, weakness, reluctance to speak, mental exhaustion, and weight loss, referred to as “overwork consumes qi.”

2. Excessive mental labor: Excessive mental labor refers to excessive thinking and worry. Excessive mental labor can consume heart blood and damage spleen qi, leading to symptoms such as palpitations, forgetfulness, insomnia, and abdominal distension, and in severe cases, it can lead to qi and blood deficiency, weakening organ functions, and even chronic diseases.

3. Excessive sexual activity: Excessive sexual activity refers to excessive indulgence in sexual activities. Normal sexual activity generally does not harm the body, but excessive sexual activity can consume kidney essence, leading to symptoms such as weakness in the lower back and knees, dizziness, mental fatigue, or in men, nocturnal emissions, reduced sexual function, or even impotence.

(2) Excessive Leisure

Excessive leisure refers to a lack of labor and exercise, leading to stagnation of qi and blood, weakness of muscles and bones, sluggish spleen and stomach, physical weakness, or obesity, and upon exertion, symptoms such as palpitations, shortness of breath, and sweating may occur, which can also lead to other diseases.