Chinese Medicine : Six Exogenous Factors

Six Exogenous Factors

Spring-wind, summer-heat, summer-fire, later summer-dampness, autumn-dryness, and winter-cold are the six variations in the climate of the four seasons. They are also known as the "six climatic factors" or the "six exogenous qi."

The human body has the ability to adapt to climatic variations. However, when bodily resistance is too low to adapt to climatic changes or if there is an abnormal altering of the weather which surpasses the body's adaptability, then the six climatic qi will become pathogenic factors bringing about the occurrence of disease. Therefore the climatic qi are all considered to be exogenous pathogenic factors.

Diseases which are not caused by exogenous pathogenic factors, but have symptoms similar to the syndromes of wind, cold, summer-heat, dampness, and dryness are termed internal heat, internal damp, internal dryness, and internal fire. These endogenous pathogenic factors are the outcome of dysfunctions of the zang and fu organs.

1. Wind

Pathogenic wind prevails in spring and is a common pathogenic factor of the common cold. It causes diseases together with other pathogenic factors, e.g., wind-cold, wind-heat, wind-damp, etc.

1) Wind is a yang pathogenic factor, characterized by upward flowing. When it attacks the human body, it often affects the upper region first.3 For example, if exogenous pathogenic wind causes a common cold, its symptoms are headache, nasal obstruction, itching or sore throat, etc., which are confined to the upper body. If pathogenic wind together with dampness induces disease the symptoms are swelling of the eyes and face.

2) Wind is characterized by outward dispersion. If pathogenic wind attacks the body, it may affect the defensive qi causing derangement in the opening and closing of pores. The clinical symptoms are fever, sweating, aversion to wind, etc.

3) Wind blows in gusts and is characterized by rapid change. In the Suwen it says, "The wind is good at traveling and undergoes change frequently."

Diseases caused by wind are marked by migrating disease location and symptoms that appear and disappear. Onset is abrupt and disappearance hasty, e.g., migrating joint pain of bi syndromes, which usually involve joint pains, and intolerable itching of urticaria.

4) Wind is characterized by constant moving. Pathogenic wind causes motor impairment or abnormal motion of the trunk or limbs manifested by convulsion, opisthotonos, spasm and tremor of the four limbs, and rigidity of the neck. In the Suwen it says, "Predominant wind causes symptoms characterized by movements."5

5) Wind is liable to associate itself with other pathogenic factors. Pathogenic wind is apt to be accompanied with cold, damp, or heat to become wind-cold, wind-damp, or wind-heat pathogenic factors.

Wind may be also associated with some pathological products such as phlegm, forming pathogenic wind-phlegm. The commonly seen symptoms caused by exogenous pathogenic wind are known as shangfeng (wind damage).

Main clinical manifestations: fever, aversion to wind, perspiration, slow and superficial pulse, dry and itching throat, cough, nasal obstruction and discharge.

These symptoms are due to damage by exogenous pathogenic wind to the body surface and the lung. If exogenous pathogenic wind attacks the skin and muscles, the wei (defensive) qi is damaged and fails to defend the body surface. So perspiration and aversion to wind occur. When wei qi fights against exogenous pathogenic wind, fever arises. When the disease locates in the exterior of the body, it causes sweating, thus the pulse is superficial and slow. When exogenous pathogenic wind attacks the lung, its function will become abnormal in the spreading and descending of qi and also brings about a dysfunction of body fluid distribution. The clinical manifestations of dry and itching throat, cough, nasal obstruction and discharge occur.

2. Cold

Pathogenic cold is prevalent in winter and as a yin pathogenic factor, it is likely to consume yang qi. It also has the characteristics of contracture and stagnation. These are described as follows:

1) Pathogenic cold, as a yin pathogenic factor, is liable to consume the yang qi of the body, producing cold syndromes. If the pathogenic cold attacks the body surface leading to a closing of the pores and obstruction of the flow of defensive yang qi, it is manifested by the symptom of aversion to cold. If pathogenic cold directly attacks the spleen and stomach it leads to the injury of spleen yang qi causing dysfunctions of the whole digestive process. The clinical manifestations are vomiting of clear water, diarrhea, coldness and pain of the epigastric and abdominal regions, pain relieved by warmth and aggravated by cold extremities, etc.

2) Pathogenic cold is characterized by contracture and stagnation. Invasion of pathogenic cold may cause contracture of the blood vessels and tendons, and obstruction of qi and blood circulation. This manifests as pain of a cold nature. Pathogenic cold may also cause a common cold with symptoms of sore aching joints and headache. Stagnation of cold in the liver channel leads to hernia of a cold nature, coldness, pain, and swelling of the testis. Pathogenic cold may also cause stomach ache, abdominal pain, etc.

Commonly seen syndromes caused by exogenous pathogenic cold are classified into: cold damaging the skin and muscle and cold damaging the spleen and stomach.

Cold Damaging the Skin and Muscle: fever, aversion to cold, no sweating, tense and superficial pulse, cough, asthma, nasal obstruction, nasal discharge, headache, and aching body.

Fever, aversion to cold, no sweating, tense and superficial pulse are caused by exogenous pathogenic cold that has blocked the spreading of wei (defensive) qi. The lung is closely related to the skin and hair. If exogenous pathogenic cold blocks the body surface and the wei qi can not spread, then lung qi fails to disperse and descend, causing nasal obstruction and discharge, cough, and asthma. Exogenous pathogenic cold will also obstruct the channels, resulting in the stagnation of qi and blood, which manifests as headache and aching body.

Exogenous Pathogenic Cold Injuring the Spleen and Stomach: vomiting, diarrhea, borborygmus, and abdominal pain.

This group of symptoms is caused by an over-intake of raw and cold food or the exposure of the abdomen to cold. As exogenous pathogenic cold injures the yang qi of the spleen and stomach, then the functions of ascending and descending qi by the spleen and stomach become disordered, causing a dysfunction of digestion and absorption with the symptoms of vomiting, diarrhea, abdominal pain, borborygmus, etc.

3. Summer-Heat

Summer-heat is the main pathogenic factor occurring only in the summer. It is a yang pathogenic factor. Its characteristics are described as follows:

1) Summer-heat is a yang pathogenic factor characterized by sweltering heat. If pathogenic summer-heat attacks the body, the clinical manifestations are yang-heat, syndromes, such as high fever, burning heat sensation of the skin, irritability, forceful and rapid pulse, etc.

2) Summer-heat consumes qi and yin (body fluid), and is characterized by upward direction and dispersion. Invasion of pathogenic summer-heat to the head region causes dizziness, vertigo, and excessive sweating due to the abnormal opening of the pores. Excessive sweating exhausts the qi and body fluid and manifests as thirst with desire to drink, dryness of the lips and tongue, constipation, yellowish and concentrated urine, etc.

3) Pathogenic summer-heat often combines with damp to cause diseases when the temperature and air humidity are very high. If summer humid-heat attacks the body, the manifestations are fever, heavy sensation of the head or even the whole body, stuffiness and fullness of the chest and epigastric regions, nausea, vomiting, abdominal distension, diarrhea, etc.

Pathogenic factors in summer are summer-heat, sun-stroke and summer humid-heat.

Main clinical manifestations of summer-heat: fever, excessive sweating, irritability, thirst with preference for cold drinks, shortness of breath, lassitude, general weakness, scanty and yellowish urine, rapid and xu (weak) pulse.

Main clinical manifestations of sun stroke: dizziness and vomiting for mild cases; sudden collapse, unconsciousness, profuse and cold sweating, cold extremities, forceful and xu pulse for severe cases.

This group of symptoms are caused by strong sun heat that internally affects the body qi activity leading to sudden prostration of qi and body fluid.

Main clinical manifestations of summer humid-heat: fever, irritability, stuffy chest, nausea, vomiting, anorexia, lassitude, loose stools, yellowish urine, soft pulse, yellow and sticky tongue coating, etc.

The symptoms resulting from summer humid-heat invasion include the common symptoms of summer-heat, such as fever, irritability, yellowish urine, etc., and the symptoms caused by the obstruction of dampened qi circulation, such as stuffy chest, nausea, vomiting and anorexia. Furthermore, there are also the symptoms of internal dampness, such as loose stools, soft pulse, sticky tongue coating, etc.

4. Damp

Damp is the main pathogenic factor causing disease in the late summer since it is the most humid and rainy season. It is a yin pathogenic factor with the following characteristics:

1) Pathogenic damp stops the functional activity of qi and leads to the injury of spleen yang. The spleen functions best in a dry environment and is susceptible to dampness, therefore pathogenic damp is liable to attack spleen yang. If spleen yang is checked by pathogenic damp, it will cause a dysfunction of transportation and transformation, and obstruct the functional activity of qi. The following symptoms will occur: distension and fullness of the epigastric and abdominal regions, anorexia, sweetish taste in the mouth, loose stool, cold extremities, etc.

2) Pathogenic damp is a substantial pathogenic factor characterized by heaviness, turbidity, viscosity, stagnation, and sluggishness. Invasion by pathogenic damp also causes the symptoms of heaviness, distension and soreness of the trunk and extremities. The secretions and excretions of the patient has foul and turbid features. The disease duration lingers.

3) Pathogenic damp is characterized by a downward direction. It is a yin pathogenic factor which often attacks the lower portion of the body. The Suwen says, "When damp attacks the body, it will affect the lower portion first."6 Clinical manifestations are ulceration and edema of the lower extremities, soreness of muscles, and joint pain of the lower limbs, etc.

Commonly seen syndromes caused by pathogenic damp are exterior damp, and damp bi.

Main clinical manifestations of exterior damp: fever, aversion to cold, fever not lowered after sweating, heaviness of the body and head, sore aching of the four limbs, white, thin and slippery tongue coating, soft and slow pulse.

Those symptoms are due to the injury of the body surface by pathogenic damp. When there is obstruction by dampness, it damages the yang qi of the body, and blocks the defensive qi. So fever and aversion to cold appear. Damp is characterized by heaviness, turbidity, and stickiness. Thus fever is not lowered after sweating. Moreover, other manifestations such as heaviness of the body and head, sore aching of the four limbs, slippery tongue coating, and soft pulse occur.

Damp bi is one of the bi syndromes due to excessive pathogenic damp, also known as fixed by syndrome.

Manifestations of damp bi: continued soreness at one location, aching and heaviness of the joints, motor impairment, and numbness of the skin.

Bi syndromes indicate the obstruction by wind, cold, or damp in the channels which damages the joints, skin, and muscles. Damp is characterized by heaviness and turbidity, so heaviness is fixed in the joints.

5. Dryness

Dryness is the main pathogenic factor in autumn. Its characteristics are as follows;

1) Pathogenic dryness is apt to consume yin, especially body fluids. Clinical manifestations are dryness of the mouth, lips and nose, dryness of the tongue, dry, rough and chapped skin, dry stool, etc.

2) Pathogenic dryness is liable to injure the lung. The lung is considered a tender organ which prefers moisture, cleanliness, and descent. If pathogenic dryness attacks the body from the mouth and nose, the yin fluid of the lung is likely to be consumed. It may lead to the dysfunction of dispersion and descent, and manifest as dry cough with scanty sputum, sticky mucus causing difficult expectoration, or bloody sputum, etc.

Commonly seen syndromes caused by pathogenic dryness are cool dryness and warm dryness.

Main clinical manifestations of cool dryness: fever, aversion to cold, headache, no sweating, dryness of the mouth and nose, dry skin, cough with scanty or no sputum, dry white and thin tongue coating.

The symptoms of cool dryness are similar to symptoms caused by exogenous pathogenic cold, but are accompanied with the symptoms of body fluid insufficiency.

Main clinical manifestations of warm dryness: fever, mild aversion to wind and cold, headache, scanty perspiration, dry cough, or cough with a small amount of sticky sputum, dry skin, thirst, irritability, red tongue tip and sides, and dry scanty tongue coating. The warm dryness syndrome is similar to the mild heat syndrome, indicating that the body fluid is exhausted.

6. Fire Heat or Mild Heat

Fire, heat, and mild heat are yang pathogenic factors. They are of the same nature but differ in intensity. Fire is the outcome of extreme heat. Mild heat is the least severe. These types of heat are sometimes termed pathogenic fire-heat or pathogenic mild heat and are characterized by an upward flaring and damaging of yin, with a tendency to disturb the blood system. The following are some special features:

1) Fire is characterized by upward flaring. Clinical manifestations are fever, thirst, profuse sweating, etc. If pathogenic fire travels inward to attack the mind, it causes irritability, anxiety, insomnia, or even mania, unconsciousness, and delirium in severe cases. Since pathogenic fire is likely to flare upward, the clinical manifestations may be mostly on the head and facial regions, such as a swelling and pain of the gums due to extreme stomach fire, ulcers of the tongue and mouth, headache, and redness, pain and swelling of the eyes.

2) Pathogenic fire is liable to consume yin fluid. Manifestations are fever, aversion to heat, accompanied by thirst with desire for drinks (especially cold drinks), dryness of throat and mouth, constipation, yellowish urine, etc.

3) Pathogenic fire may disturb the blood and cause extravasation. Mild cases will only have rapid pulse due to acceleration of blood circulation. In severe cases, the blood vessels and collaterals may be damaged, manifesting various hemorrhagic symptoms, such as vomiting of blood (hematemesis), nose bleeds (epistaxis), blood in the urine or stool, excessive menstrual flow, skin eruptions, external boils and ulcers, etc. The common syndrome caused by fire (heat) at the early stage is exterior-heat syndrome.

Main clinical manifestations: fever, mild aversion to cold, headache, sore throat, thirst, yellowish urine, dry stool, red tip and sides of the tongue, superficial and rapid pulse, etc. These symptoms are due to the invasion of fire (heat) on the body surface which consumes body fluids.

This concludes the discussion of the effect of the six exogenous pathological factors on the body. In general, these factors first damage the body surface and then manifest an exterior syndrome with the symptoms of fever and aversion to cold.