What is allergic purpura dermatitis caused

Allergic purpura dermatitis is of unknown etiology. There are reports of familial onset. Patients are often accompanied by factors such as increased local venous pressure, such as varicose veins of the lower limbs or prolonged standing, resulting in poor venous return of the lower limbs. Due to increased vascular permeability, erythrocyte overflow and collapse, hemosiderosis occurs. Some people think it is an allergic disease caused by focal infection. Allergic purpura dermatitis lesions initially miliary size, round or polygonal purpuric papules, smooth surface, rust color, pressure does not fade, long into yellow brown, skin lesions scattered or fused into pieces, the edge is not clear. Predilection sites for the leg, thigh, and lower trunk. Self-conscious symptoms are more varying degrees of itching.