Purpura is commonly seen in allergic purpura and thrombocytopenic purpura. Purpura growing on the legs will cause certain harm to joints, kidneys, urinary system and so on. 1. Joints: If purpura grows in the joints, it may lead to swelling of the joints, and if not treated in time, it may cause mobility disorders and other hazards. 2. Kidney: Purpura on the legs may cause abnormal proteinuria and other pathological changes, and in severe cases, it may even cause serious damage to the kidneys. 3. Urinary system: purpura on legs may be caused by thrombocytopenia, if not treated in time, hematuria may occur, which may cause serious effects on the urinary system. Therefore, to summarize, purpura on the legs is a more serious phenomenon, we must go to the hospital in time to check the diagnosis, early treatment, to avoid causing greater harm.