EXTERNAL
Six Exogenous factors
Wind- Prevails in spring, as do “Wind” diseases. Exposure to the wind after sweating, or sleeping in a draught, are important inducing factors in being affected by pathogenic Wind.
Wind, characterised by upward and outgoing dispersion, is a Yang pathogenic factor. When it invades the human body from outside, it often attacks the upper portion of the body, weakening the defensive Qi and causing derangement in the opening and closing of pores over the body surface. Clinical symptoms are headache, nasal obstruction, soreness or itching of the throat, facial puffiness, aversion to Wind, and sweating.
Wind occurs in gusts and is characterised by rapid change, pathogenic Wind being especially so. Diseases caused by Wind are marked by migrating pain, their symptoms and signs appearing and disappearing. Onset is abrupt and disappearance sudden, eg the migratory joint pain of rheumatic arthritis and urticaria.
Wind is characterised by constant movement.
Pathogenic Wind tends to move constantly, causing abnormal motion or rigidity of the trunk or limbs. Clinical manifestations are convulsion, spasm and tremor of the four limbs and stiffness of the neck. Opisthotonos in tetanus and deviation of the eyes and mouth in facial paralysis are both related the this characteristic of pathogenic Wind.
Wind is apt to associate itself with other pathogenic factors. Pathogenic Wind is apt to associate itself with Cold, Damp, Dryness, or Heat and form complex pathogenic factors of Wind-Cold Wind-Damp, Wind-Dryness, or Wind-Heat. Wind may also be associated with Phlegm, producing a Wind-Phlegm syndrome.

Cold
Pathogenic Cold is prevalent in winter, as are diseases of cold. In the cold season, too little clothing, exposure to cold after sweating, and being caught in wind and rain provide chances for the development of pathogenic Cold.
Cold is a Yin pathogenic factor and is likely to consume Yang Qi. Cold is a manifestation caused by excess Yin and therefore is a Yin pathogenic factor. When the Yang Qi of the body is consumed by Cold, it will lose its normal function of promoting body warmth, and clinical manifestations of Cold will appear, such as chills, shivering , cold limbs, pallor, diarrhea with undigested food in the stool and clear urine in increased volume.
Cold is characterised by contraction and stagnation. Invasion by pathogenic cold may cause contraction of channels and collaterals and retardation of circulation of Qi and Blood. Symptoms are pain of a cold nature and numbness of extremities. Cold may also cause closing of pores with manifestation of chills and anhidrosis.

Summer Heat
 Diseases caused by pathogenic Summer Heat occur only in Summer. Onset is often due to prolonged exposure to blazing sun on hot days, or staying in a hot room with poor ventilation.
Summer Heat consumes Qi and Yin and may disturb the Mind.
Summer heat is a Yang pathogenic factor. Its features are upward direction and dispersion. Invasion of summer Heat may cause excessive sweating, thirst, shortness of breath, lassitude, and concentrated urine. In severe cases, there may be high fever, restlessness, red dry skin, and such mental symptoms as abrupt onset of delirium or coma.
Summer Heat often combines with Damp to cause disease, as rain often accompanies the Heat of summer. Manifestations are dizziness, a heavy sensation of the head, suffocating feeling in the chest, nausea, poor appetite, diarrhea, and general sluggishness.

Damp
Pathogenic Damp often occurs in damp seasons. Such diseases usually follow the wearing of clothing wet with rain or sweat, dwelling in a low-lying and Damp place, or being in frequent contact with water during work.
Damp is characterised by heaviness and turbidity. Damp is a substantial pathogenic factor which is weighty in nature. Its invasion of the body often gives rise to such symptoms as heaviness and a sensation of distension in the head, as though it were tightly bandages. There is also dizziness, general lassitude, fullness in the chest and epigastrium, nausea, vomiting, and a stickiness and sweetish taste in the mouth.
Pathogenic Damp is foul in nature, Its invasion often causes skin diseases, abscesses and oozing ulcers, massive leukorrhea of purulent nature with foul odor and turbid urine.
Damp is characterised by viscosity and stagnation.
Diseases caused by pathogenic. Damp are often lingering. Fixed Bi syndrome = rheumatoid arthritis, and epidemic encephalitis.

Dryness
Invasion of pathogenic dryness often occurs in late autumn when moisture is lacking in the atmosphere.
Pathogenic dryness is apt to consume Yin fluid, especially the Yin of the Lung. Clinical manifestations are dry, rough and chapped skin, dryness of the mouth and nose, dryness and soreness of the throat, dry cough with little sputum.

Heat
Heat, Fire and mild heat are all Yang pathogenic factors. They are of the same nature but different in intensity. Among them, Fire is the most severe and mild Heat the least severe.
Heat, like Summer Heat, is also characterised by dispersion, damaging Yin with a tendency to go inward to disturb the mind. The following are some special featured of Heat.
Invasion by Heat is apt to stir up Wind and cause disturbance of blood. Excess of pathogenic Heat exhausts the Yin of the Liver and causes malnutrition of the tendons and channels. Manifestations are high fever accompanied by coma and delirium, convulsion, stiffness of the neck, opisthotonos, and eyes staring upwards. This is known as ‘extreme Heat stirring up the Wind.’ Pathogenic Heat may cause extravasation by disturbing the Blood. Manifestations of hemorrhage may appear, such as hematemesis, epistaxis and skin eruptions. This is called ‘excessive Heat disturbing the Blood.’
Invasion by Heat tends to cause skin infection.  Surgical cases, such as carbuncle, furuncle, boil and ulcer with local redness, swelling, hotness and pain are caused mainly by pathogenic Heat.

Pestilential Factor- Causes epidemic diseases. It is similar to pathogenic Heat in nature, but more pernicious and more fierce in pathogenicity as it is usually complicated with contagious toxic pathogenic Damp. Pestilential diseases are often mortal, with rapid and drastic changes as seen in smallpox, plague and cholera.
Five Endogenous factors- These are diseases that are not caused by exogenous pathogenic Wind, Cold, Damp, Dryness and Heat, but whose clinical manifestations are similar to diseases caused by them. In order not to confuse the two categories of disease, the pathological changes of such cases are referred to as endogenous Wind, Cold, Damp, Dryness and Heat.

INTERNAL
Seven Emotional Factors- are the main cause of endogenous disease. Emotions are appropriately named as they are energy in motion.
These are Joy, Anger, Melancholy, Meditation, Grief, Fear and Fright.
The seven emotions are reflections of man’s mental state as induce by various stimulations in his environment. They are physiological phenomena and will not cause disease under normal conditions.
However, if the emotions are very intense and persistent or the individual is hypersensitive to the stimulations, they may result in drastic and long-standing change in emotion which leads to disease.
Diseases caused by the seven emotional factors often show dysfunction of the Zang-Fu organs and disturbance in circulation of Qi and Blood.
Different emotional changes selectively injure different Zang-Fu organs.
Anger injures the Liver = Outward movement. The corresponding human sound is shouting. Excessive anger may cause dysfunction of the Liver in promoting unrestraint patency of vital energy and give rise to pain and distension in the costal and hypochondriac region, irregular menstruation, mental depression and irascibility. If the function of storing Blood is impaired, hemorrhage may result.
Anger is not always negative, and has its place as one of the emotions that one should be capable of expressing.
Joy, in excess and fright injure the Heart = Upward movement. Excessive joy or fright may cause mental restlessness and give rise to palpitation, insomnia, irritability, anxiety, and even mental disorders.  Joy requires excitement and stimulation, rather than a feeling of inner contentment and peace. Too much joy er excitement will cause the energy to rise and scatter, and may produce a condition known as “floating Shen” or “the spirit not housed”.
Grief and Sadness injures the Lung = Contracting movement. The contraction of energy with sadness has the same effect on the body, often resulting in a feeling oppression in the chest and consequent rounding of the shoulders,  which is the posture through which a person can be visibly known to be sad. The Lungs have an expanding energetic function, and this sadness opposes this.
Mediation injures the Spleen = Centering movement. The earth is the center, and governs thought. In its negative state, its expression is muddled and directionless, leading to worry. This causes a knotting and stagnation of Qi, which impairs the transforming and transporting function of the Spleen. In its positive aspect the Spleen provides the ability to communicate.
Fear injures the Kidney = Descending movement. Excessive grief, melancholy and mediation may cause dysfunction of the spleen and Stomach in transportation and transformation, and cause anorexia and abdominal fullness and distension after meals.

Clinically, disorders caused by the seven emotional factors are seen mainly in the Heart, Liver and Spleen.

MISCELLANEOUS PATHOGENIC FACTORS
Irregular Food Intake
Voracious eating, or over-eating of raw or cold food. These may impair the function of the Spleen and Stomach in transportation, transformation, reception and digestion of food and cause nausea, vomiting, belching of foul air, acid regurgitation, epigastric and abdominal pain with distension, borborygmus and diarrhea.
Indulgence in alcoholic drink or greasy, highly flavored food. These may produce Damp-Heat or Phlegm-Heat which first injures the Spleen and Stomach. Dysfunction of vital organs may result from aggravation of the situation.
Too little nourishment intake. Too little nourishment intake may be due to lack of food, weakness of the Spleen and Stomach which hinders nourishment intake by affecting digestion and absorption, or limited variety of food owing to personal preference. Prolonged under supply of food results in malnutrition and insufficiency of Qi and Blood, with resulting emaciation, lassitude, dizziness, blurring of vision, palpitation and even syncope.
Intake of insanitary food. Intake of food contaminated by poisonous materials or of stale food may impair the function of the Spleen and Stomach or cause intestinal parasitic diseases.

Over-strain and stress or lack of physical exertion
There is an old saying in China: ‘Running water does not go stale and door-hinges do not become worm eaten.’ In other words, constant motion may prevent things from rotting, and physical exertion is important to life. However, prolonged over straining may lead to illness due to consumption of the anti-pathogenic factor and give rise to signs of feebleness such as emaciation, lassitude, excessive swearing, palpitations, dizziness and blurring of vision.
Lack of  physical exercise or necessary physical exertion may cause retardation of circulation of Qi and Blood, general weakness, lassitude, obesity and shortness of breath after exertion. It may also lower the general resistance of the body.
Excessive sexual activity injures the Qi of the Kidney and causes manifestations of poor health. Backache, weakness of the limbs, dizziness, tinnitus, impotence, lassitude and listlessness are some of these.

Traumatic injuries
 Included are incisions, gunshot injuries, contusions, sprains, scalds and burns, and insect or animal stings and bites.

Stagnant Blood and Phlegm
Both stagnant Blood and Phlegm involve the following two aspects:
 1. Substantial: Stagnant Blood and Phlegm may refer to pathological products, eg. extravasated Blood clot and sputum. They are secondary pathological factors which will lead to further pathological changes if not eliminated in time.
 2.Insubstantial: Stagnant Blood and Phlegm are sometimes pathological concepts generalising the characteristics of the clinical symptoms and signs. For example, a case of epilepsy with coma and rattle in the throat can be diagnosed from the characteristics of the clinical manifestations as the “Heart being misted by the Phlegm”.
Stagnant blood
Local stagnation of blood due to circulatory retardation from various causes and extravasated blood held in spaces between tissues or in cavities or tract are substantial stagnant blood. It may remain stagnant in different parts of the body and cause different functional disturbances.
Disorders caused by stagnant blood are characterised by:
Pain- This may be stabbing or boring, or at times it is severe colicky pain. The painful area is fixed.
Hemorrhage. The Blood is often deep or dark purplish, or it has dark purple clots.
Ecchymoses or petechiae. These take the form of purplish spots on the skin or the tongue.
Mass tumor, or enlargement of the internal organs in the abdomen.

Phlegm
Function disorder of the Lung, Spleen and Kidney may cause derangement of water metabolism, eliciting abnormal distribution of body fluid, a part of which is condensed into Phlegm. When Phlegm is formed, it may stay in different parts of the body and result in different syndromes:
Phlegm-Damp affecting the Lung: cough, asthma and expectoration of excessive sputum
Phlegm misting the Heart: coma and rattle in the throat.
Phlegm blocking channels and collaterals: hemiplegia, deviation of the eyes and mouth and numbness of limbs.
Phlegm retained subcutaneously: This takes the form of soft, movable nodules.

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