Pathogenic Factors of Exogenous Origin

Pathogenic factors of exogenous origin refer to diseases that arise from the natural environment, primarily invading the body through the skin and respiratory tract. These mainly include the Six Excesses (Liù Yín) and pathogenic qi.

Six Excesses The Six Excesses refer to the six types of exogenous pathogenic factors: Wind (Fēng), Cold (Hán), Heat (Shǔ), Dampness (Shī), Dryness (Zào), and Fire (Huǒ). These are different climatic conditions in nature, which under normal circumstances are referred to as “Six Qi”. The continuous movement and change of the Six Qi determine the different climates of the four seasons: spring wind, summer heat (fire), late summer dampness, autumn dryness, and winter cold. In daily life, people not only experience the characteristics of these changes but also develop certain adaptive abilities through their own regulatory mechanisms, allowing physiological activities to align with the changes in the Six Qi. Therefore, the Six Qi generally do not cause disease. However, when climatic changes are abnormal, such as excessive or insufficient Six Qi, or when the Qi appears out of season (e.g., cold in spring when it should be warm, or cold in autumn when it should be cool), or when climatic changes are too abrupt (e.g., sudden cold or heat), exceeding the body’s adaptive capacity, or when the body’s resistance to disease decreases and cannot adapt to climatic changes, the Six Qi then become pathogenic factors, leading to disease. At this time, the “Six Qi” is referred to as the Six Excesses. The term “Excesses” implies an overabundance or infiltration. The Six Excesses refer to abnormal Six Qi, which are considered improper Qi, hence also called Six Evils (Liù Xié).The pathogenicity of the Six Excesses has the following common characteristics.Exogenous Nature: The Six Excesses invade the human body, primarily through the skin and respiratory tract, or both pathways simultaneously, leading to disease. Since the Six Excesses are mostly acquired from the outside, they are termed “exogenous Six Excesses”. The diseases caused are referred to as “exogenous diseases”.Seasonality: The diseases caused by the Six Excesses often have significant seasonality, such as more wind diseases in spring, heat diseases in summer, damp diseases in late summer, dryness diseases in autumn, and cold diseases in winter, commonly referred to as “seasonal diseases”. This is a general rule.Regionality: The diseases caused by the Six Excesses are often closely related to the living environment, with different regions exhibiting different disease characteristics. For example, the northwest region has more cold and dryness diseases, while the southeast coastal region has more damp and warm diseases.Environmental Factors: The diseases caused by the Six Excesses are often closely related to the living and working environment. Generally, in the northwest plateau region, where the terrain is high and the weather is cold, there are more cold and dryness diseases; in the southeast coastal region, where the terrain is low and the temperature is relatively high with high humidity, there are more damp and heat diseases; those who live in damp areas or work on water are prone to damp diseases; those who work in high temperatures are prone to dryness and heat diseases.Combination: The Six Excesses can cause disease individually, but they can also combine in pairs or more to invade the body and cause disease. For example, wind-cold colds, damp-heat diarrhea, and wind-cold-damp bi syndrome.Transformation: During the disease process, the Six Excesses can not only influence each other but can also transform into one another under certain conditions. For example, cold evil can transform into heat, and prolonged heat and dampness can transform into dryness. Transformation does not mean that one type of evil in the Six Excesses becomes another type, but rather that the nature of the symptoms caused by the Six Excesses changes, often related to the body’s own constitution.In addition, there are certain pathological changes that are not caused by the exogenous Six Excesses but are due to dysfunction of the organs, qi, blood, and body fluids, leading to internal transformations of wind, cold, dampness, dryness, heat, and fire. To distinguish them from exogenous Six Excesses, they are referred to as “internally generated Five Evils”, namely internal wind, internal cold, internal dampness, internal dryness, and internal fire (internal heat). Since they often interact with exogenous Six Excesses during the disease process and have similar characteristics and pathogenic manifestations, they are also discussed in this section.1Characteristics and Pathogenic Features of Wind Evil Wind is the primary qi of spring. Although wind evil is most common in spring, it can also occur in other seasons.Wind evil primarily invades the body through the skin and is the most common pathogenic factor among the Six Excesses, often serving as a precursor to cold, dampness, dryness, and heat evils, hence it is called the “leader of the Six Excesses”.Wind evil is an important and widespread pathogenic factor in exogenous diseases.(1)Wind is a yang evil, its nature is to open and disperse, easily attacking yang positions: Wind is characterized by movement and does not settle, possessing the properties of lightness, rising, and outward movement, thus it is classified as a yang evil. Opening and dispersing means that wind easily causes the pores to open, leading to the outward leakage of qi and fluids, resulting in symptoms such as sweating and aversion to wind. It easily attacks yang positions, meaning that wind evil often invades the upper parts of the body (head and face), yang meridians, and the skin, lungs, etc., commonly resulting in symptoms such as aversion to wind and cold, fever, headache, nasal congestion, throat itching, and pain in the back and neck.(2)Wind is characterized by rapid movement and frequent changes: Rapid movement means that wind has the characteristic of being active and not settling, making the location of the disease move and change unpredictably. For example, “moving bi” (also known as wind bi) presents as migratory joint pain, with pain that is not fixed. Frequent changes mean that wind evil has the characteristics of rapid onset and quick changes. For instance, the rash in urticaria, skin itching, appears unpredictably, reflecting the rapid change characteristic of wind.(3)Wind is proactive: Wind’s proactive nature means it can cause objects to move, thus its pathogenic effects can lead to symptoms resembling movement, such as dizziness, chest movement, and convulsions, all related to wind evil.(4)Wind is the leader of all diseases: The term “leader” refers to the beginning or the first. This indicates that wind evil often carries other evils with it, serving as a precursor to external evils causing disease.Due to wind’s nature of opening and dispersing, cold, heat, dampness, dryness, and fire evils often attach to wind and invade the body, such as wind-cold, wind-heat, wind-damp, and wind-dryness.Secondly, wind evil is extremely widespread, occurring in all four seasons, and can invade the body in various ways, leading to a multitude of diseases. Ancient texts even referred to wind evil as a general term for pathogenic factors of exogenous diseases.2Characteristics and Pathogenic Features of Cold Evil Cold is the primary qi of winter.In winter, the temperature is cold, and there are often sudden drops in temperature. If the body does not adequately protect against the cold, it is easy to be affected by cold evil.Cold evil can also be felt in other seasons, such as sudden drops in temperature, sweating in the wind, getting wet in the rain, exposure to cold, or consuming cold food and drinks.Cold can cause two types of harm: exterior cold and interior cold.Cold evil harms the skin and obstructs the defensive yang, known as “exterior cold”; when cold evil penetrates the interior, it harms the yang qi of the organs, known as “interior cold”.(1)Cold is a yin evil, easily harming yang qi: “Excessive yin leads to cold” indicates that cold is a manifestation of excessive yin, thus its nature is classified as yin. Cold evil, being excessive yin, can obstruct yang qi, leading to a struggle between the internal yang qi and cold, which inevitably depletes a significant amount of yang qi; when yang qi is damaged, it loses its normal warming and transforming functions, resulting in cold symptoms. For example, when cold evil attacks the exterior, the defensive yang is obstructed, leading to symptoms such as fever, aversion to cold, and absence of sweating; when cold evil penetrates the interior, damaging the spleen yang, symptoms such as abdominal pain, vomiting, and diarrhea may occur.(2)Cold is characterized by stagnation: When cold evil invades the body, excessive yin harms yang, leading to the meridians losing warmth, causing qi and blood stagnation, which results in pain. For example, severe pain in the head and neck, joint pain in cold bi syndrome, and severe joint pain in painful bi syndrome are all related to the stagnation caused by cold.(3)Cold causes contraction: Contraction refers to the action of pulling or drawing in. When cold evil invades the body, it causes the qi mechanism to contract, leading to the contraction and tightness of the pores, meridians, and tendons. For example, when cold evil attacks the exterior, it causes the skin pores to contract, sweat pores to close, leading to symptoms such as aversion to cold, fever without sweating, etc.; when cold invades the meridians and joints, it causes the tendons to contract and become painful, leading to difficulty in joint movement.(4)Cold is characterized by clarity: Secretions or excretions that appear clear and thin are often caused by cold evil. For example, in the early stages of a wind-cold cold, clear nasal discharge may occur; when cold evil obstructs the lungs, it may lead to clear and thin phlegm.3Characteristics and Pathogenic Features of Heat Evil Heat is the primary qi of summer, transformed from fire and heat.Heat evil has a clear seasonality, primarily occurring from the summer solstice to the beginning of autumn.Heat evil is purely an external evil, with no internal heat, which distinguishes it from the other five evils of the Six Excesses.(1)Heat is a yang evil, its nature is fiery: The nature of heat is to burn and ascend, thus it is classified as a yang evil. When yang is excessive, heat symptoms such as high fever, aversion to heat, flushed face, and rapid pulse are common. When heat evil invades the body, symptoms are often seen in the upper parts of the body, such as headache, flushed face, sore throat, bleeding gums, swollen gums, or ulceration of the mouth and tongue.(2)Heat easily disturbs the mind: The heart belongs to the fire element in the five elements, and the heart is the center of the five organs. The nature of heat evil is yang and agitated, thus it easily disturbs the mind. Mild cases may present as restlessness and insomnia; severe cases may lead to confusion, agitation, and delirium.(3)Heat easily depletes qi and injures fluids: Heat is a yang evil, and when yang is excessive, it leads to yin diseases. First, heat forces fluids to leak out, causing excessive sweating, which depletes fluids; second, heat evil burns and consumes yin fluids, leading to symptoms such as thirst, dry throat, short and red urine, and constipation. When heat forces fluids to leak out, qi also follows the fluids, leading to symptoms of qi deficiency, such as fatigue, weakness, and low energy; in severe cases, it can lead to a critical state of qi collapse and yin damage, resulting in life-threatening situations.(4)Heat easily generates wind and stirs blood: Excessive heat generates wind, also known as “extreme heat generates wind”, is caused by the burning of the liver meridian by heat evil, which consumes yin fluids, leading to internal wind movement, resulting in symptoms such as high fever, confusion, convulsions, stiff neck, and upward gaze. Excessive heat stirs blood, which is caused by heat entering the blood, leading to chaotic blood flow, and can even burn the blood vessels, resulting in various bleeding disorders such as hemoptysis, epistaxis, excessive menstruation, and metrorrhagia.(5)Heat easily causes swelling and sores: Heat evil invades the blood level of the body, leading to local accumulation, eroding flesh and causing sores and abscesses. Clinical manifestations may include local redness, swelling, heat, pain, and pus formation.Pathogenic Qi Pathogenic qi, also known as epidemic qi, is a type of highly infectious external evil. In TCM literature, pathogenic qi is also referred to as “epidemic poison”, “epidemic qi”, “strange qi”, “evil qi”, “toxic qi”, and “malignant qi”. Pathogenic qi differs from the Six Excesses; as stated in the “Treatise on Epidemics”, “the disease of epidemics is not caused by wind, cold, heat, or dampness, but by a different kind of strange qi in the world.” This indicates that pathogenic qi is distinct from the Six Excesses. The diseases caused by pathogenic qi are epidemic diseases, which actually include many modern infectious diseases and severe infectious diseases.1Characteristics of Pathogenic Qi(1)Rapid onset, severe condition: Diseases caused by pathogenic qi have a short incubation period, and can even lead to immediate illness upon contact, with severe and rapidly changing conditions and high mortality rates. For example, diphtheria, epidemic dysentery, smallpox, etc., all have rapid onset, fierce progression, and critical conditions. In severe cases, if not rescued in time, death can occur within hours of onset. Generally, diseases caused by the Six Excesses are less acute than those caused by internal injuries, while diseases caused by pathogenic qi are even more acute and severe than those caused by the Six Excesses.(2)Strong infectivity, easy to spread: The most significant characteristic of pathogenic qi is its strong infectivity. Pathogenic qi primarily spreads through the air, invading the body through the mouth and nose. Additionally, it can spread through contaminated food, contact, insect bites, and other forms of contact with pathogens, leading to outbreaks. The “Treatise on the Origins of Diseases” clearly states the serious harm of pathogenic qi to humans, stating, “When people are affected by malignant qi, the disease qi easily spreads, even leading to the extinction of families.”(3)One qi, one disease, similar symptoms: Pathogenic qi is highly specific; the disease qi differs from the Six Excesses, phlegm, and blood stasis. For example, wind evil can cause “common cold” but can also lead to “wind rash”, “bi syndrome”, “dizziness”, and various other diseases, with different symptoms. There are many types of pathogenic qi, but each type of pathogenic qi only causes one epidemic disease, and the clinical symptoms of each epidemic disease are basically consistent. Therefore, the “Treatise on Acupuncture” states: “When the five epidemics arrive, they all easily infect each other, regardless of size, and the symptoms are similar.”2Factors Influencing the Occurrence and Spread of Epidemics The occurrence and spread of epidemic diseases are related not only to the strength of the body’s righteous qi but also to the following factors.(1)Climatic factors: Abnormal changes in the natural climate, such as prolonged drought, extreme heat, excessive rain, flooding, humidity, and miasma, can promote the growth and spread of pathogenic qi, leading to the outbreak of epidemics.(2)Environmental and dietary factors: Poor environmental hygiene, such as water or air pollution, can easily breed epidemic toxins; animal carcasses not buried in time, and improper disposal of waste can also promote the growth of epidemic toxins; food contamination and unclean eating can also lead to the occurrence and spread of epidemics.(3)Preventive measures: Prevention and isolation are effective measures to prevent the occurrence of epidemics and control their spread. Because pathogenic qi is highly infectious, patients with epidemic diseases should be isolated and treated immediately to prevent the spread of the epidemic. For those at risk of infection, preventive medications should be administered, and attention should be paid to diet and lifestyle to maintain righteous qi and enhance the body’s resistance.(4)Social factors: The occurrence and spread of epidemics are closely related to social systems and conditions. Social unrest, continuous wars, natural disasters, poverty, and backwardness can all lead to a low capacity to resist natural disasters, making epidemics more likely to break out and spread. Conversely, if a country is stable, economically prosperous, and the people live and work in peace, with attention to hygiene and epidemic prevention, the incidence of epidemics will significantly decrease, and outbreaks will be less likely.

Electronic Textbooks

Traditional Chinese Medicine — Human Health 8th Edition