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Six excesses, as the main external cause of diseases, is a collective term for external pathogenic factors: wind, cold, summerheat, dampness, dryness, and fire — also called six climatic pathogenic factors. The six excesses share common properties in causing diseases: exogenous, seasonal, transformable, combinable, regional and environmental as listed in Fig. 5-2.

Fig. 5-2 Common properties of six excesses

The six excesses can act either alone or in a combination of two or more pathogenic factors in attacking the human body. Such syndromes as common cold of wind-cold type is an example of medical problems caused by wind and cold combined. Furthermore, in the course of a disease, six excesses can not only influence each other, but also transform into one another.

Wind as a pathogenic factor is characterized by its rapid movement, swift changes, and ascending and opening actions. Wind is likely to invade the yang sites of the body such as upper, back or body surface, because wind is yang pathogen, and the onset of the disease caused by wind is usually sudden.* Wind is known as a leading pathogen. Other pathogens, such as cold, dampness, dryness and heat, often attach themselves to wind when they launch invasions into the human body.

Cold as a pathogenic factor is characterized by the damage to yang qi, deceleration* of activity, congealing* and contracting* actions. Cold pertains to yin category, and therefore, can slow down the metabolism and damage yang qi. When the body is attacked by cold, the interstices* and sweat pores are closed, and therefore, there is no sweating. If cold is retained in joints, pain with fixed location is sure to occur.

Summerheat* as a pathogenic factor only occurs in summer, and is characterized by hotness and evaporation. There is only exogenous summerheat and no endogenous* summerheat. Summerheat by nature is hot and flames upward. When summerheat attacks the human body, there will be high fever, sweating, flushed face*, dry mouth, dizziness and vertigo*. Additionally, summerheat often attacks patients with dampness.

Dampness as a pathogenic factor is characterized by its impediment to* movement and its turbidity, heaviness, stickiness and downward flowing properties. Dampness is apt to* inhibit qi dynamic and damage yang qi because of its impediment nature. When attacked by dampness, the patient feels as if he /she were bearing a heavy load and the patient may have symptoms of a heavy head with the feeling of being swathed, heavy body, and sluggish or heavy limbs. Dampness often attacks the lower part of the body as it is heavy; disease caused by dampness is difficult to cure because it is sticky.

Dryness is apt to injure the lungs and impair body fluids. When dryness attacks the body, it is marked by thirst, scanty* urine, dry cough, and scanty and sticky phlegm.**

Fire as a pathogenic factor is characterized by intense heat that is apt to injure fluids, consume qi, engender wind, induce bleeding, and disturb mental activities.* The fire pathogen tends to enter the heart and disturbs mental activities. Disease caused by fire is manifested by* thirst with desire for cold drinks, tiredness, or mental disorder. When fire invades the human body, it is apt to enter the liver meridian, consuming fluid; as a result, the sinews and vessels can not be nourished and moistened. Then, the syndrome of internal stirring of liver wind* occurs, manifested by high fever, coma*, upward squint of the eyes*, and convulsion. Furthermore, when fire enters the blood and stagnates in a local area, it is likely to cause sores and ulcers*.

Pestilential qi is a pathogen that causes epidemic infectious disease. The diseases caused by pestilential qi are characterized by their sudden onset, strong infectious ability, and rapid spreading with high mortality*. Epidemic pathogens can attack the human body through many routes, in all ages, and both sexes. There are many kinds of pestilential qi and every one has its own specificity and property, causing a specific syndrome. Certain pestilential qi can cause certain epidemic diseases.