Purpura dermatitis, also called allergic purpura, is caused by various allergens to increase the permeability of blood vessels, which causes the limbs and trunk to appear dense bleeding spots, also known as vasculitis. For this situation: first, to remove allergens, avoid eating fish, shrimp, meat, eggs, milk and other kinds of food to stimulate it. Second, you can apply antihistamines, such as cetirizine, calcium, vitamin C, which can promote absorption. Third, for purpura nephropathy, purpura nephritis, and arthritis, you can give glucocorticoids for treatment, and add vitamin C to promote the absorption of blood vessels. The disease is a benign disease, the prognosis is still relatively good.