Allergic purpura is manifested in patients with simple purpura, skin lesions can usually appear in the initial stage of the disease, while renal lesions appear 1 week or even longer after the onset of the disease, so simple purpura may also appear as the disease progresses with the possibility of allergic purpura nephritis. Allergic purpura is a group of autoimmune diseases with necrotizing small vasculitis as the characteristic change, its clinical manifestations can be divided into five types: simple type, abdominal type, joint type, renal type, mixed type, etc. The simple type is the most common clinical manifestation, manifesting as skin purpura, purpura, which can occur repeatedly and does not fade after 1-2 weeks. And the renal type is the most serious state in allergic purpura, which can reappear within 1 week after the appearance of purpura, manifesting as proteinuria, hematuria, edema and hypertension. Therefore, for patients with allergic purpura manifesting as simple cutaneous purpura, they need regular review of urine routine to assess whether purpura nephritis occurs.