Allergic cutaneous vasculitis is an allergic inflammatory skin disease mainly involving small superficial dermal blood vessels caused by a variety of reasons, occurring in the limbs, with the calves and ankles especially prominent. Clinical manifestations include papular purpura, wind, small water, polymorphic erythema, small nodules, erythema and nodules are more common, the course of the disease is chronic, and can be prolonged up to a few years. This disease often occurs in young men and women, possible triggers include bacterial and viral infections and certain drug factors, given the diverse forms of the disease, the course of the disease is long, such as early and clear diagnosis can help shorten the course of the disease, reduce the pain and improve the efficacy of treatment. The disease is known by more names, including allergic cutaneous arteritis, nodular dermal allergy, nodular necrodermatitis, and allergic vasculitis, and is pathologically characterized by leukocyte-crushing vasculitis. Etiology and pathogenesis This disease is currently believed to be caused by a variety of factors resulting in a type of allergic reaction, which is caused by immune complexes deposited in the wall of small blood vessels, activation of complement and vascular damage. Factors include: 1, infection; 2, drugs; 3, xenoproteins or chemical agents; 4, certain systemic diseases such as SLE, SS, RA, etc.; 5, malignant tumors and so on. Clinical manifestations 1, young adults, mostly acute onset, the onset is often accompanied by fever, fatigue and joint pain and other systemic symptoms, and skin damage occurs soon; 2, the skin occurs in both calves and ankles, and can be developed to both thighs, buttocks, and even all over the body; it is symmetrical; 3, the skin damage is polymorphic, and the initial damage is hemorrhagic maculopapular and purpura, and erythema, papule, and wind cluster can appear in the course of the lesion, Blisters, blisters, blisters, nodules, necrosis and ulcers, etc., of which purpura, nodules, necrosis and ulcers are the most typical features; 4, after the rash is cured, there may be hyperpigmentation or superficial atrophic scarring. Involvement of mucous membranes can occur nosebleeds, blood in the stool, etc.; some patients can be involved in internal organs known as cutaneous-systemic vasculitis, such as the kidneys, gastrointestinal machine nervous system, etc., so that the corresponding clinical manifestations, suggesting that the condition is more serious. Local symptoms may include itching, pain or burning sensation. 5, the disease has a tendency to self-healing, the course of the disease is generally 2 ~ 4 weeks, but Kofa Fukuda attack. Initial skin lesions for the millet size red macules and purpura; laboratory tests can be accompanied by anemia, platelet reduction, neutrophil increase. Blood sedimentation increased, complement decreased and hyperglobulinemia, involving the kidneys can appear proteinuria and microscopic hematuria, a few patients ANCA positive. Diagnosis: according to the skin damage is prevalent in both calves and ankles, the characteristics of skin damage (purpura, nodules, necrosis and ulceration), the age of onset is young adults, combined with histopathology, the diagnosis can be clearly defined; Differential Diagnosis: Henochromatosis purpura, which is most common in children and adolescents, the lesions are mainly purpura or with an eruption-like rash, usually without nodules and necrosis, which may be accompanied by joint pain, gastrointestinal symptoms and protein and red blood cells in the urine. The disease is relatively mild. Treatment 1, acute stage should be bed rest, find and remove the cause of the disease, avoid all kinds of triggering factors; 2, drug treatment: oral or intravenous application of vitamin C; according to the condition can be used Pansentin, anti-inflammatory pain, aminophenyl sulfone, colchicine, or Lei Gongteng polyglucoside and so on. Severe cases or those with systemic damage need to add corticosteroids. The infected person should be given antibacterial treatment at the same time. 3, local therapy is mainly based on the lesions symptomatic treatment.