The way to check allergens in urticaria is to conduct allergen testing, which includes patch test, prick test, serum allergen screening and so on. 1. Plaque test: the suspected substances that may cause allergy are directly applied to the patient’s skin surface and observed for a certain period of time to find out whether there is allergy or not, and the test process usually takes about 48~72 hours. 2. Prick test: Specific reagents are injected into the skin by prick method to determine whether there is any allergy through local skin changes, and the test result is usually within 24 hours. 3. Serum Allergen Screening: Blood is drawn to detect allergens directly, but only for some allergens, not covering all of them, and has a certain reference significance. Since the types of allergens are more complicated, you can ask your doctor to choose the appropriate test method according to your clinical manifestations after an interview.