Dermatological purpura is the general term for extravasation of red blood cells from blood vessels and bleeding within the skin and mucous membranes. The small and superficial ones are called petechiae, the larger and deeper ones are called petechiae or petechiae, blood accumulates in the tissues, swelling and fluctuating is called hematoma, the rash is flush with the skin surface or slightly elevated, usually purple, and the deep dermal bleeding is cyanotic. Due to the change of extravasated red blood cell hemoglobin, it can produce red, purple, blue, brown or yellow in sequence and finally fade. There are many reasons for the occurrence of purpura, which are generally grouped into two categories: vascular system lesions and disorders of coagulation mechanisms, but often the result of a combination of factors, such as purpura of infectious diseases, which can be vascular, platelet-based or coagulation disorders. Therefore, the clinical treatment plan should be specific to the specific cause.