Endogenic fire-toxin and heat-toxin are collectively referred to as the fire-toxin.The fire-toxin is both a pathological product and a pathogenic factor.The pathogenic characteristics of the fire-toxin have attracted extensive attention and research in traditional Chinese medicine.The imbalance in the physiological function of Zang-fu,the damage in transportation and transformation of Qi-blood-body fluid,all these phenomena lead to a specific pathological state of human body.In this pathological state,the pathogenic factors (such as wind,heat,phlegm,blood stasis,etc.) are brewed and changed,turning into heat,then fire,finally the fire-toxin.This process is from quantitative change to qualitative change.Once the fire-toxin is formed,its cruel force destroys the substance of human body.Based on this prominent characteristic,the fire toxin is a key link in emergent occurrence,mutation,and evolvement of critical diseases,also a major cause of deterioration and refractoriness in refractory diseases.