Urticaria is a limited edematous reaction due to dilation and increased permeability of small blood vessels in the skin and mucous membranes. It is characterized clinically by a sudden onset and rapid fading of wind clumps of varying size that leave no trace of itching after fading. It is very common and occurs at least once in the lifetime of 15-20% of the population, and can occur at any age, mostly in adults. There are many factors that cause urticaria, the cause is more complex, about 3/4 of patients can not find the cause, especially chronic urticaria. The common causes are: 1, food such as fish, shrimp, eggs, milk is the most common; followed by meat and certain plant foods, 2, drugs can be divided into two categories: one is the formation of antigenic drugs, such as penicillin, serum, vaccines, sulfonamide, dysentery, etc.; the other is histamine releasing agents, such as aspirin, morphine, codeine, dulcolax, etc.. 3, infection Various infectious factors can cause the disease, the most common is the virus and Staphylococcus aureus that cause upper respiratory tract infection; followed by hepatitis, infectious mononucleosis and coxsackie virus. 4. Inhalants Pollen, dust, animal dander, smoke, feathers, fungal spores, volatile chemicals (such as formaldehyde, acrolein, pyrethrum, cosmetics, etc.) and other airborne allergens, etc. 5, physical factors such as cold, heat, sunlight, friction and pressure and other physical and mechanical stimuli. 6, animal and plant factors such as insect bites, and contact with nettles, wool, etc. 7, mental factors mental tension or excitement, after exercise caused by acetylcholine release. 8, genetic factors Some types of urticaria are related to genetics, such as familial cold urticaria, hereditary familial urticaria syndrome, etc. 9, visceral and systemic diseases such as rheumatic fever, rheumatoid arthritis, systemic lupus erythematosus, etc.