The sudden appearance of a bag on the body that looks like a mosquito bite is likely to be urticaria or papular urticaria. Urticaria is mostly manifested as recurrent red spots, windy bumps and rashes all over the body, which usually subside on their own within 24 hours, and are self-conscious of itching. The disease may be related to allergies (e.g., food, medications, etc.), infections (e.g., bacteria, viruses, parasites, etc.), physical factor stimuli (e.g., sunlight, cold, heat, pressure, etc.), psychiatric factors, insect bites, and hereditary factors, among other things. Pemphigus urticaria occurs in spring and fall, also known as insect bite dermatitis, the typical rash is characterized by scattered fusiform, windswept pimples on the trunk and extensor sides of the limbs, some of which have pseudopods, and the center of which may have blisters, and individuals may have blisters, with severe self-conscious itching, and old and new lesions often coexisting. The new and old lesions often coexist. Generally, it can subside after 1-2 weeks, and after subsiding, hyperpigmentation spots can remain.