The formation of urticaria is mainly due to a variety of causes leading to a variety of inflammatory cell activation and degranulation, the release of inflammatory mediators, the mechanism of activation can be divided into immune and non-immune. 1. Immune mechanism: most of them are type I hypersensitivity, type II hypersensitivity usually occurs in blood transfusion-induced urticaria, and type III hypersensitivity is common in serum sickness and urticarial vasculitis. 2. Non-immune mechanisms: mainly due to the toxic effects of certain molecules, complement, physical factors, etc. through the mast cell surface receptor and ligand direct action thus leading to cell activation. Inflammatory cell activation after the release of histamine, cytokines, arachidonic acid and other inflammatory mediators, thus causing increased vascular permeability, etc., so that the skin, the respiratory tract and so on a series of allergic phenomena, the occurrence of urticaria should be timely consultation.