Heat is one of the six pernicious influences on the health of the body within the Chinese medical framework. The nature of Heat is to accelerate metabolic activity, dilate blood vessels and activate circulation. Heat tends to rise and move out towards the surface.
As an external influence (normally termed External Fire), it appears suddenly, being experienced as excessive body heat, dislike of heat and a preference for cold. It may be accompanied by high fever, rapid pulse, red face, red eyes, and dark reddish urine. Such febrile illnesses were often life threatening. Symptoms include boils, carbuncles and other reddish skin lesions. Fire Poison is the collection of Heat in parts of the body (called inflammation in Western medicine). Its symptoms are carbuncles, boils and red, swollen, raised and painful skin lesions. Fire pernicious influence can also produce symptoms associated with overheating and dehydration, such as thick mucous, scanty urine, burning sensations, thirst, constipation, agitation, etc. Because Fire induces reckless movement, particularly of Blood and Shen, Excess Fire may produce haemorrhage or skin eruptions (in the case of Blood) or confused speech or delirium associated with fever (in the case of Shen).
As an internal influence (normally termed Heat), the signs are less severe and indicate a Deficiency of Yin.