The six climatic factors are pathogenic wind, pathogenic cold, pathogenic summer-heat, pathogenic dampness, pathogenic dryness and pathogenic heat (fire).
Wind, cold, summer-heat, dampness, dryness and heat (fire) are six kinds of natural climatic factors known as "six qi". Human beings living in the natural world constantly contact with these natural factors. Under normal condition, the human body can adapt to the changes of climate which are indispensable to the existence of human beings. If the harmonious relationship between human beings and nature is broken, the body is unable to adapt itself to the changes of the climate, leading to the occurrence of disease. Under such condition, the six natural climatic factors become pathogenic factors.
The six climatic factors are characterized by the following features in causing disease:
(1) The cause of disease by the six climatic factors is usually related to seasonal changes of living conditions.
(2) The six climatic factors may singly or collectively attack people. For example, pathogenic wind may combine with cold, dampness, dryness and heat to attack people and lead to wind-cold syndrome, wind-dampness syndrome, wind-dryness syndrome and wind-heat syndrome.
(3) The nature of the diseases caused by the six climatic factors may be the same as or different from that of the six climatic factors. For example, invasion of pathogenic cold may deepen internally to transform into heat and so do accumulation of pathogenic dampness. Sometimes the nature of the disease caused by various pathogenic factors may vary due to the differences in constitution, which is called "secondary transformation". For example, frequent abundance of yang or frequent deficiency of yin may transform into heat after the invasion of exogenous pathogenic factors; frequent abundance of yin or frequent deficiency of yang may transform into cold after invasion of exogenous pathogenic factors; frequent abundance of dampness or deficiency of the spleen may lead to transformation of dampness, etc.
(4) The six climatic factors usually invade people from the skin into the muscles or from the mouth and nose into the lung and the defensive qi. That is why external syndromes tend to appear at the early stage of disease caused by the six climatic factors and gradually transmit to the internal.
Besides, clinically there are some diseases due to dysfunction of the viscera that appear similar to the pathological changes caused by pathogenic wind, pathogenic cold, pathogenic dampness, pathogenic dryness and pathogenic heat (fire), known as "five endogenous pathogenic factors", such as endogenous wind, endogenous cold, endogenous dampness, endogenous dryness and endogenous heat (fire) which are not directly caused by, but can result from, the six exogenous climatic factors. For example, attack by exogenous pathogenic wind can stir the endogenous pathogenic wind and exogenous pathogenic dampness can induce endogenous pathogenic dampness.
Wind is the main climatic factor in spring. That is why wind tends to cause disease in spring. But in other seasons wind also can cause disease. Wind is characterized by the following features:
1. Wind tends to float
Wind is a pathogenic factor of yang nature, characterized by floating and dispersion because of lightness. That is why wind attacks the upper part (the head and face) and skin first when it invades the body. So the disease caused by wind mainly involves the surface of the body, the head and the face with the manifestations of headache, running nose, sweating and aversion to cold, etc.
2. Wind tends to move
Wind is mobile and the disease caused by it is also changing(such as migratory pain of limbs in wind-bi syndrome), tremor of the limbs (such as convulsion, spasm due to some special pathogenic factors of wind) and dizziness (such as subjective feeling of shaking or faintness or like sitting in a boat or car). Dizziness is usually caused by dysfunction of the viscera complicated by liver-wind. Exogenous pathogenic wind is often the factor that induces endogenous wind.
3. Wind tends to change
Wind tends to change. So the disease caused by wind is often characterized by sudden onset, immediate transmission and change as well as fast healing. For example, rubella is marked by quick fluctuation of cutaneous pruritus without a fixed location.
4. Wind tends to be complicated by other pathogenic factors
Since it is easier for wind to attack the body, other factors in the six exogenous factors often attach themselves to wind when they invade the body, frequently leading to exogenous wind-cold syndrome, exogenous wind-heat syndrome, exogenous wind-dampness syndrome and exogenous wind-dryness syndrome. That is why TCM holds that "wind is the leading cause of all diseases".
Cold is the dominant climatic factor in winter. So cold diseases, though may encounter in other seasons, are usually emerged in winter. The invasion of cold into the body is commonly due to cold weather and lack of cold control measures. Sometimes it is due to drench, walking in water and exposure to wind when sweating.
The invasion of wind is either superficial or internal. The former refers to external cold syndrome caused by cold attacking the surface of the body and stagnates the defensive qi while the latter refers to direct attacks of internal of the body and impairs the visceral yang-qi.
The following is a brief description of the nature of pathogenic cold and its characteristics in causing diseases.
1. Cold tends to impair yang
Cold pertains to yin and tends to impair yang. When cold attacks the surface of the body, it will impair yang in the superficies; when it attacks the internal of the body, it will impair the visceral yang. If yang-qi is impaired and cannot warm and transform qi, it will lead to cold syndrome due to functional decline. If cold impairs the superficies, the defensive qi will be stagnated, leading to aversion to cold and anhidrosis; if cold directly invades the spleen and the stomach, the spleen-yang will be impaired, leading to cold pain in the stomach and abdomen, vomiting and diarrhea; if cold directly attacks shaoyin, it will impair heart-yang and the kidney-yang, leading to aversion to cold, lying with the knees drawn up, dispiritedness, cold hands and feet, diarrhea with undigested food, profuse and clear urine, thin and indistinct pulse.
2. Cold tends to coagulate
Qi, blood and body fluid flow continuously inside the body because they are constantly warmed and propelled by yang-qi. If the pathogenic cold obstructs yang-qi, then qi, blood and body fluid cannot flow freely and will coagulate in the vessels, bringing pain. If cold attacks the viscera, the visceral qi and blood will be stagnated, causing abdominal pain; if cold attacks the muscles and joints, qi and blood in the muscles and joints will coagulate, resulting in pain in the muscles and joints.
3. Cold tends to contract
Cold pertains to yin and tends to restrain the activity of qi, leading to contracture of muscles, tendons and vessels. If cold attacks the superficies, the muscular interstices will be stagnated, the muscles will be contracted and the defensive qi cannot disperse, leading to aversion to cold, anhidrosis and papules; if cold invades the limbs and joints, the tendons and vessels will become contracted, bringing on somatic pain, headache and spasm of the limbs.
Summer-heat is transformed from heat and fire in summer. Summer-heat pertains to yang and usually appears after summer solstice and before autumn solstice. The attack by summer-heat is either due to hot weather or due to low adaptability of the body to the environment.
Summer heat is characterized by the following features：
1. Summer-heat is hot
Summer-heat pertains to yang and is hot in nature. So the disease caused by summer-heat is usually marked by a series of yang symptoms such as high fever, dysphoria, reddish complexion, thirst with preference for cold drink and full and large pulse, etc.
2. Summer-heat tends to disperse
Summer-heat pertains to yang and tends to disperse and elevate. Summer-heat disturbs the mind when it elevates, leading to dysphoria and dizziness or even sudden coma and unconsciousness in severe cases. Summer-heat induces sweating and consumes body fluid when it disperses, leading to thirst with preference for drinking water and reddish ancl scanty urine. If there is profuse sweating, qi will get lost, eventually bringing on shortness of breath and lassitude due to qi deficiency.
3. Summer-heat is often complicated by dampness
In hot season, heat fumigates dampness. That is why dampness is exuberant in summer and often mixes up with heat to attack people. Thus disease caused by summer-heat-dampness is often, apart from fever and extreme thirst, characterized by lassitude of the four limbs, chest oppression, vomiting and unsmooth loose stool, etc.
Dampness is predominant in late summer but also can be encountered in other seasons. Since it is hot in late summer, dampness permeates everywhere due to fumigation and frequently causes disease. Sometimes drench or living in damp area also results in disease of dampness.
The following is a brief description about the nature and characteristics of dampness in causing disease:
1. Dampness is heavy and turbid
Dampness pertains to yin, so it is heavy. The attack by dampness will lead to symptoms as heaviness of the body or the four limbs, heaviness of the head like being bound, or heaviness and lassitude of the whole body. Dampness is similar to water and it often mixes up with water. That is why it is turbid. Invasion of dampness into the body often brings on the symptoms of turbid secreta and excreta, dirty complexion, excessive secretion of gum in the eyes, loose stool, mucous and bloody dysentery, turbid urine, leukorrhea and oozing eczema.
2.Dampness tends to block qi
Dampness moves slowly because it is heavy. So it tends to retain in the viscera and meridians, inhibits the flow of qi and disturbs the activity of qi, frequently leading to chest oppression and fullness, scanty and unsmooth urination and inhibited defecation. On the other hand, dampness pertains to yin and tends to impair yang-qi. Thus prolonged blockage of qi by dampness will prevent yang-qi from flowing, often causing exuberance of dampness and decline of yang. Since dampness pertains to earth in the five elements and is related to the spleen, it tends to impair the spleen, bringing on encumbrance of the spleen by dampness and stagnation of qi in the middle energizer. If dampness impairs yang, it will inactivate spleen-yang and further accumulate water and dampness, leading to diarrhea, scanty urine, edema and ascites.
3. Dampness is sticky and stagnant
These characteristics of dampness usually affect people in two ways. One is that the disease caused by dampness is not brisk. For example, the secreta and excreta are too sticky to be excreted. The second is that the disease caused by dampness is obstinate and recurring with long duration, such as damp-bi syndrome (damp-blockage syndrome), eczema and damp-warm syndrome.
4. Characteristic of dampness being descending and apt fixed to attack yin locations
Dampness is similar to water and characteristic of descending and apt to attack the lower part of the body. For example, edema caused by fluid-dampness is usually seen in the legs; vaginal discharge, turbid urine, diarrhea, dysentery and cankerous legs and mostly caused by down-pour of dampness.
Dryness is predominant in autumn. So disease caused by dryness mostly appears in autumn. In late summer dampness permeates. But in autumn dampness disappears and the weather becomes cool and dry. Dryness can be divided into warm-dryness and cool-dryness due to difference in weather. The disease occurring at the early stage of autumn is a kind of warm-dryness because there is still some remaining summer-heat; the disease occurring at the late stage of autumn is a kind of cool-dryness syndrome because the weather is already cold in late autumn.
The following is a brief description of the nature and characteristics of dryness in causing disease:
1. Characteristic of dryness being dry and puckery and apt to impair fluids
When invading the body, it is most apt to impair fluids, resulting in various xerotic symptoms such as dry mouth, nose and throat or even chaps, lusterless hair, dry stools and scanty urine and so on.
2. Dryness likely to injure lung
As a tender viscus, the lung governs qi and respiration. It opens into the nose and is externally connected with skin and hair. The lungs are fond of clarity and moist and averse to dryness. Dryness pathogen frequently invades the human body through the mouth and nose and attacks the lungs, causing dry cough, scanty or sticky phlegm, gasping pain in the chest; when it damages the lung vessels, there is bloody sputum. The lung and large intestine are in exterior and interior relationship, so the failure of lung qi to disperse and descend and exhaustion of body fluids will result in lack of moistening of the large intestine and its dysfunction to transport, manifested as dry stools.
Heat(fire) is the predominant climatic factor in summer. So disease due to pathogenic heat (fire) usually occurs in summer. However it can also be encountered in other seasons. Since there are two ways to describe the order of pathogenic factors in Huangdi Neijing, namely "wind, cold, summer-heat, dampness, dryness and heat" and "wind, cold, summer-heat, dampness, dryness and fire", so "fire" and "heat are often mentioned in the same breath. If we make a comparison between the fire and the heat, we can say that the heat is the manifestation of the fire and the fire is the nature of the heat. They are, to a certain degree, different from each other but intrinsically related to each other.
The following is a brief description of the nature and the characteristics of heat (fire) in causing disease:
1. Heat(fire) tends to flame up
Heat(fire) pertains to yang and tends to flame up. So the disease caused by the pathogenic heat(fire) is marked by high fever, aversion to heat, extreme thirst, sweating and full pulse. When the pathogenic heat (fire) attacks the body, it may disturb the mind, leading to dysphoria, insomnia, mania, coma and delirium, etc. Since the pathogenic heat is responsible for irritability and rapid movement, the disease caused by it is characterized by acute onset and rapid transmission.
2. Heat(fire) tends to consume qi and impair body fluid
Heat(fire) pertains to yang and tends to consume yin-fluid. If there is superabundant heat, it will drive body fluid out of the body in the form of sweat. So the disease caused by the pathogenic heat, apart from the manifestations of heat, is often accompanied by thirst with preference for drinking water, dry throat and tongue, dark and scanty urine and retention of dry feces due to consumption and impairment of body fluid.
3. Heat(fire) tends to cause convulsion and bleeding
Convulsion means that when fire-heat invades the body, it burns and scorches liver meridians, exhausts fluids, causes the loss of nourishment of tendons and muscles, resulting in the syndrome of liver wind stirring up internally. So it is also called "extreme heat causing wind", clinically manifested as high fever, coma, spasm of limbs, upward squint of the eyes and opisthotonus etc...
Bleeding means that when fire enters blood vessels, it accelerates blood flow and burns the vessels, causing abnormal flow of blood, manifested as various bleeding, such as hemoptysis, epistaxis, hematochezia and hematuria, echymosis, excessive menstruation, metrorrhagia and metrostaxis etc...
4. Heat(fire) tends to cause sores and abscesses
Fire invade xuefen, stagnates in local areas, causing erosion of muscles and pus, which are termed as sores, ulcers or abscesses. Clinically, it marked by are redness, swollen, burning and painful sensation in the local areas.
Pestilence is a kind of strong infectious pathogenic factor, quite similar to the pathogenic heat(fire) in the six pathogenic climatic factors in nature, but more serious than the pathogenic heat in toxicity. The diseases caused by pestilence are marked by acute onset, severe pathological condition, similar symptoms, strong infection and easiness to spread. Historical records show that diseases caused by pestilence often spread the disease far and wide with high mortality.
The commonly encountered diseases caused by pestilence are facial erysipelas, mumps, pestilent dysentery, diphtheria, scarlet fever, smallpox, cholera and plague.
Five endogenous pathogenic factors
The so-called five endogenous pathogenic factors are endogenous wind, endogenous cold, endogenous dampness, endogenous dryness and endogenous heat (fire). Though they are called wind, cold, dampness, dryness and heat (fire), they are actually pathogenic factors due to dysfunction of the viscera. That is why the word "endogenous" is used to modify their names.
- Endogenous wind
Endogenous wind is produced by the liver, so it is usually called "liver-wind" and "internal disturbance of liver-wind". There are four factors responsible for the occurrence of endogenous wind. The first is extreme heat producing wind, referring to the disease marked by convulsion due to exuberant heat that scorches liver-yin and deprives the tendons of nourishment; the second is transformation of liver-yang into wind, referring to the disease marked by dizziness and infantile convulsion resulting from hyperactivity of yang transforming into wind and disturbing the upper orifices; the third is yin-deficiency stirring wind, referring to the disease marked by infantile convulsion and convulsion resulting from declination of liver-yin and inability of yang to hide that lead to failure of the yin-fluid to nourish the tendons; the fourth is blood-deficiency stirring wind, referring to the disease marked by muscular peristalsis and tremor resulting from failure of the deficient blood to nourish the liver and the tendons.
- Endogenous cold
The occurrence of endogenous cold is due to the deficiency of yang. The deficiency-cold of the viscera can be caused by either the deficiency of the kidney-yang or the spleen-yang or heart-yang. Since the kidney-yang is the source of yang-qi in the whole body, the deficiency of the kidney-yang is the predominant factor responsible for the occurrence of endogenous cold.
- Endogenous dampness
Endogenous dampness results from the spleen. Usually failure of water to transform due to dysfunction of the spleen may produce the endogenous dampness which encumbers the spleen and affects the transporting and transforming functions of the spleen or accumulates into phlegm and retention of fluid, further resulting in other diseases.
- Endogenous dryness
Endogenous dryness results from insufficiency of body fluid and is related to yin-deficiency. Since body fluid and blood can transform into each other, the deficiency of blood also causes dryness. The manifestations of endogenous dryness are often related to the intestines, the stomach, the lung and other orifices, such as dry nose, dry throat, dry eyes, scanty urine and retention of dry feces, etc.
- Endogenous heat(fire)
The causes of endogenous heat (fire) are various, such as exogenous wind, exogenous cold, exogenous dampness and exogenous dryness that all can transform into heat; mental upset and extreme changes of emotions that often turn into fire; predomination of yang and deficiency of yin that usually produce the endogenous fire and heat; and excessive qi that frequently leads to fire, etc.