Cold and heat are two principles used to differentiate the nature of diseases. Cold and heat nature of diseases are the reflection of the conditions of yin and yang in the body. Yin predomination or yang asthenia leads to cold syndrome; while yang predomination or yin asthenia leads to heat syndrome. Syndrome differentiation of cold and heat is helpful for understanding the nature of disease and providing evidence for selecting warming therapy or clearing therapy.

Cold syndrome  
Cold syndrome refers to symptoms caused by yang asthenia or yin predomination due to invasion of cold pathogenic factors or various other factors. This syndrome is usually caused by internal exuberance of cold due to invasion of cold pathogenic factors or excessive intake of cold food, or by consumption of yangqi due to internal impairment and chronic disease. Cold syndrome may be further divided into external cold syndrome, internal cold syndrome, asthenic cold syndrome and sthenic cold syndrome according to the causes and location of pathological changes.
 
Clinical manifestations:
The clinical manifestations vary with different types of cold syndromes. The usual ones are aversion to cold or aversion to cold with preference for warmth, cold limbs and huddling up in sleeping, pale or light colored complexion, moist mouth without thirst, thin sputum, saliva and snivel, clear and profuse urine, loose stool, light colored tongue with whitish moist and slippery fur, slow or tense pulse.

Analysis of symptoms:
Attack by pathogenic cold and stagnation of yangqi or insufficiency of yangqi to warm the body lead to aversion to cold or aversion to cold with preference for warmth, cold limbs, huddling up in sleeping, light colored or pale complexion~ exuberant internal cold? and non-consumption of body fluid account for moist mouth without thirst; failure of asthenic yang to warm and transform fluid leads to clear sputum, snivel, saliva and urine; encumbrance of the spleen by pathogenic cold or asthenia of splenic yang causes loose stool. Light colored tongue with whitish slippery and moist fur and slow or tense pulse are the signs of yang asthenia and internal predominance of yin cold.

Heat syndrome  
Heat syndrome refers to symptoms due to attack by yang heat or various other factors or yin asthenia. This syndrome is usually caused by invasion of exogenous yang heat, or by interior transmission of heat transforming from pathogenic cold, or by transformation of fire from emotional upsets, or by transformation of heat from improper diet, or by internal generation of asthenic fire resulting from excessive coitus, internal impairment due to overstrain, exhaustion of yin essence as well as yin asthenia and yang sthenia. Heat syndrome may be further divided into external heat syndrome, internal heat syndrome, asthenic heat syndrome and sthenic heat syndrome according to the cause and location of diseases.

Clinical manifestations:
The manifestations vary with different types of syndromes. The usual symptoms are fever, aversion to heat with preference for cold, flushed complexion or flushed cheeks, thirst with preference for cold drinks, restlessness and insomnia, yellowish and sticky sputum and snivel, vomiting blood and epistaxis, scanty brownish urine, dry feces, reddish tongue with scanty moist and fast pulse, etc.

Analysis of symptoms:
Predomination of yang heat or yin asthenia and yang sthenia leads to internal exuberance of asthenic heat and causes fever and aversion to heat with preference for cold; fire tends to flame up drives qi and blood to flow upwards, leading to flushed complexion or flushed cheeks; consumption of body fluid by exuberant heat or deficiency of yin fluid gives rise to thirst with preference for cold drinks and scanty and brownish urine; heat disturbing the heart spirit results in restlessness and insomnia; body fluid scorched by heat causes yellowish and thick sputum and snivel; heat impairing blood vessels and driving blood to extravasate brings about hematemesis and epistaxis.

Consumption of body fluid by exuberant heat or deficiency of yin fluid gives rise to thirst with preference for cold drinks and scanty and brownish urine; heat disturbing the heart spirit results in restlessness and insomnia; body fluid scorched by heat causes yellowish and thick sputum and snivel; heat impairing blood vessels and driving blood to extravasate brings about hematemesis and epistaxis; consumption of body fluid by exuberant heat? or deficiency of yin fluid deprives the intestines of lubrication and proper transmission and leads to dry feces; reddish tongue with scanty fluid and fast pulse are signs of exuberant heat impairing body fluid.