The skin will grow red, if the skin can subside on its own within 24 hours, but other parts of the new red bun, that is hives, commonly known as “allergies” “rubella block”. Note that this disease is an allergic disease, not what people call “rubella” or “measles”, the latter two are infectious diseases. Urticaria is not contagious, but only an abnormal immune status in the body. In fact, it is difficult to clearly explain what people generally consider as allergies in medical terms. Allergy (hypersensitive) is a state of hypersensitivity of a specific organism to a variety of allergens that exist inside and outside the body, this allergic state can be long or short, short if it is just a few days, long if it can be months or even decades. Most allergens inside and outside the body cannot be seen or felt, so it is difficult to detect them. Some people, even if they are allergic to a substance at this moment, may only have a normal moderate response in the future and not produce allergic symptoms, or form immune tolerance and no longer be allergic. Zhao Yulei, Department of Dermatology, Nanjing First Hospital Allergies have nothing to do with whether hygiene at home. Another large category of common allergic diseases is dermatitis eczema-like diseases. A decades-long tracking study abroad showed that the chances of atopic dermatitis in the children of families in developed countries with good health and economic conditions were much higher than the chances of atopic dermatitis in the children of families in less developed countries with poor economic and health conditions. In our country, on the whole, children with allergic diseases are higher in urban than in rural areas, and higher in the east than in the west. Therefore, it is important to correctly understand the phenomenon of allergy. There are many children with immature and unstable immune status, which will improve as they grow older.