The cause of purpura is not yet clear, and may be due to infection, drugs, heredity, environment and other factors. Allergic purpura is one of the common vasculitis, which can be caused by the body’s allergic reaction to certain sensitizing substances, resulting in increased capillary fragility as well as permeability. The etiology and pathogenesis of purpura are not yet clear, and may be caused by infection, drugs, genetics, environment and other factors, including the following: 1. It may be caused by infections, such as bacteria, viruses and parasites. 2. It may be caused by drugs, such as antibiotics, antipyretic and analgesic drugs, sulfonamides, atropine, diuretics and so on. 3. Due to genetic factors. 4. Pollen, dust, vaccination, cold stimulation and other factors may induce allergic purpura. Patients with allergic purpura may have different degrees of purpura, mostly located in the limbs, buttocks and other parts of the body. The rash is initially a purplish-red papule, which does not fade when pressed, and may be accompanied by itching, pain and other symptoms. The rash may gradually merge into patches as the disease progresses. Once a patient is diagnosed with purpura, he or she should actively cooperate with the doctor to take relevant treatment measures to avoid delaying the condition.