The diagnosis of urticaria can be judged by the clinical symptoms of the patient. The basic damage of this condition starts as red papules or rash, rice grain to soybean size or larger, and then gradually increases or fuses into patches of various shapes and sizes, bright red or dark red in color, while the differential diagnosis of urticaria and erythema-like rash, seborrheic dermatitis, and pityriasis rosea should be strengthened. Differential diagnosis: (1) Erythema-like rash: It is a very common symptom of many skin diseases. (2) Seborrheic dermatitis: the edges of erythema are not very distinct, the basal infiltration is light, the scales are few and thin, they are yellowish and greasy, and there is no film phenomenon and punctate bleeding after scraping. (3) rose pityriasis: it occurs in the trunk and the proximal end of the extremities, is most oval small patches, its long axis is arranged along the direction of the ribs and skin lines, the scales are fine and thin. Most patients can heal themselves after a few weeks, not easy to recur after fading. The onset of the disease often starts with a mother spot, and then gradually increases. (4) Erythema multiforme-like rash: Erythema multiforme is an acute self-limiting inflammatory skin disease, often accompanied by mucosal damage, the rash is polymorphic, and the typical damage is target-shaped or iris-like damage. It can be caused by a variety of reasons, and can be related to infection with bacteria, viruses (especially simple vesicular virus), enzyme bacteria, protozoa, and also by certain drugs, such as sulfonamides, bactoids, salicylates and biological products causing the disease, and others related to cold. (5) Discoid lupus erythematosus: It occurs on the face, especially on the cheeks and the back of the nose, with a butterfly-shaped distribution. The erythema is well-defined and capillary dilatation is visible on the surface. The scales are adherent scales and adhere closely to the erythematous plaques, and when the scales are peeled off, the dilated hair follicle mouth can be seen underneath, and there are many spiny keratinous protrusions on the bottom surface of the scales. The course of the disease over time, can be seen in the center of the damage atrophy depression, pigment changes. (6) chronic eczema: can often be manifested as erythema, covered with scales, especially in the lower legs. However, chronic eczema is mostly accompanied by intense itching, the lesions are symmetrical on both sides, the degree of infiltration is heavier than psoriasis, the surface scales are thin, not silvery white, the base is red, and there may be oozing.