Allergic purpura can lead to the appearance of red papules on the feet, the symptoms of itchy bumps, is caused by the body occurs type III allergic reaction led to inflammation around the capillaries and blood vessel walls. The cause of allergic purpura is more complex, can be caused by bacteria, viruses, food, barbiturates and other drugs, the pathogenesis of type III allergic reaction, the body’s blood vessel wall antigen and antibody combination of immune complex deposition, activation of the complement, resulting in increased permeability of the blood vessel wall, resulting in the appearance of red pimples on the feet, pimples itchy. In addition, purpura may also appear joint swelling and pain, abdominal pain and other symptoms. It is recommended that patients with purpura go to the hospital in time and receive symptomatic treatment under the guidance of the doctor.