Hives are a common clinical allergic skin disease. Food, inhalant or drug allergies can cause hives, and infections can also induce hives. The cause of urticaria is not easy to determine. To find the allergen, keep a food diary, such as which foods were consumed before each attack. If you have the same food every time, it is more likely that you are allergic to that food. It is also possible to find out what medications were taken within 2-3 weeks before the rash started, and which medications caused the hives. In addition to medication history, allergen testing can also be done. Allergens are mainly food and inhalant allergies, such as eggs, milk, fish, shrimp, cat hair, dog hair, and dander are all common allergens. If the test result is positive, it also indicates allergy.