六淫

The Six Evils — wind (风, fēng), cold (寒, hán), summer-heat (暑, shǔ), dampness (湿, shī), dryness (燥, zào), and fire (火, huǒ) — are the six normal climatic influences considered as causes of disease. In their natural rhythm they are simply the "six qi" of the seasons; only when they become excessive, deficient, or arrive out of season do they become pathogenic. The term yín (淫) means "overflowing," "excessive," "deviant."

Each pathogen has its characteristic signs and tendencies, and in real cases they typically combine — wind-cold, wind-heat, damp-heat, cold-damp, and so on. They can also transform into one another over time; an externally contracted cold pathogen, for example, often "transforms into heat" once it has lodged in the interior. The six evils typically enter through the skin, hair, mouth, or nose, beginning as exterior patterns and progressing inward if not resolved. Recognizing the signature of each pathogen is the first step in diagnosing externally contracted disease.

Wind (风, fēng): "the chief of the hundred diseases." Wind is light, ascending, dispersing, swift, and constantly changing. It enters most often through the skin and hair and is frequently the vehicle by which the other pathogens make their way into the body. Cardinal signs: aversion to drafts, fever, sweating, headache, nasal congestion, and symptoms that wander from one location to another. Most common in spring.

Cold (寒, hán): cold, congealing, and contracting. Cold damages yang qi, congeals the meridians (causing pain), and contracts the pores (preventing sweating). Cardinal signs: marked aversion to cold, absence of sweating, headache and body aches, cold extremities, a pale tongue with a white coating, and a floating-tight pulse. Most common in winter.

Summer-heat (暑, shǔ): blazing hot, ascending and dispersing. It readily damages both qi and fluids and is frequently combined with dampness in humid weather. Cardinal signs: high fever, profuse sweating, irritable thirst, shortness of breath, fatigue, and scanty dark urine. Summer-heat is the only one of the six pathogens that occurs only in its proper season (the hot months); the others can arise out of season.

Dampness (湿, shī): heavy, turbid, sticky, and downward-tending. Damp encumbers the Spleen and obstructs the smooth movement of qi. Cardinal signs: heaviness of the body, a head that feels "wrapped in a cloth," chest oppression, poor appetite, loose stools, and a greasy tongue coating. Damp diseases are characteristically lingering and slow to resolve. Most common in late summer.

Dryness (燥, zào): dry and astringing, readily damaging body fluids — and most readily damaging the Lung, the most delicate of the zang. Cardinal signs: dryness of the mouth and nose, dry cracked skin, dry cough with little sputum, and dry stools. Most common in autumn. It is further subdivided into cool dryness (cooler weather, with combined cold) and warm dryness (warmer weather, with combined heat).

Fire and heat (火/热, huǒ/rè): blazing and ascending, readily damaging qi and fluids, readily stirring wind and disturbing the blood, and readily generating swellings and sores. Cardinal signs: high fever, marked thirst, flushed face, irritability, constipation, dark urine, a red tongue with a yellow coating, and a rapid pulse. Fire and heat name the same family of patterns at different intensities; fire is heat carried to its extreme.