Heat (fire) is one of six climatic pathogenic factors (ie. a quality in the environment or climate which can cause disease). It is the predominant climatic factor in summer and so diseases caused by it usually occur in summertime. However it can also occur in the other seasons.
In TCM, “heat” and “fire” are often mentioned in the same breath. If we make a comparison between fire and heat, we can say that fire is a severe form of heat, and that heat is the beginning of the fire. They are, to a certain degree, different from each other but also intrinsically related to each other. Diseases caused by pathogenic heat (fire) manifest symptoms such as high fever, aversion to heat, extreme thirst, sweating and full pulse. Heat (fire) also tends to consume qi and dry up body fluid. It tends to produce wind and disturbs the blood and so can be the cause of convulsions and bleeding.