The most commonly applied definition of disease is the deviation from the normal form and function of the human body. Specifically, disease refers to the process of abnormal life activity of the organism due to the disturbance of the self-stabilizing regulatory system under the action of certain etiological conditions, and this process can trigger a series of metabolic, functional and structural changes, which can be manifested by patients as symptoms, signs and abnormalities of mental behavior. Disease is an extremely complex process, in many cases from health to disease is the process from quantitative to qualitative change, when external pathogenic factors act on the body cells, reach a certain intensity and last for a certain period of time, that is, the accumulation of a certain amount of pathogenic factors, it will cause cell damage, the damaged cells will appear functional, metabolic, morphological and structural disorders.