This is a question to which it is difficult to have a definitive answer. Although modern medicine believes that the following conditions must be present for the development of allergic diseases: (1) a person with a sensitive constitution (related to genetic and long-term environmental factors); (2) exposure to antigens (exogenous proteins) that can cause the body to produce allergic reactions. However, this general answer obviously does not explain why a particular individual develops an allergic disease. In fact, there are many unknown and uncertain factors that contribute to the development of allergic diseases. From a genetic point of view alone, taking allergic rhinitis (AR) as an example, it is currently believed that the mode of inheritance of AR is polygenic, i.e., many phenotypic shapes of the disease are determined by multiple genes acting in concert rather than a single gene, and the mode of inheritance is neither autosomal dominant nor recessive, nor X-linked, but there is a tendency for family aggregation. The answer is so uncertain in the face of genetic factors, which are one of the many factors leading to allergic diseases, and medicine is even more powerless in the face of more complex and diverse environmental factors, such as air pollution, diet and nutrition, microbial infections, etc. Patients often report that they have symptoms related to allergic diseases and even have elevated levels of IgE antibodies in their blood, and take anti-allergy drugs with certain effect, but no clear allergenic substances can be identified. This is because there are many environmental substances that can cause allergies in the body, but there are only a limited number of several hundred target substances that are currently included in the clinical examination, so it makes sense that no definite answer can be given. A woman in her 40s once had recurrent facial swelling and itching for a while, and finally found out that she was allergic to wheat flour, saying that I had eaten wheat flour for 40 years and had never been allergic before. I can’t eat it anymore! The good thing is that sometimes, this allergy is just a special reaction of the body at a certain time, and after some time or after treatment, it may return to normal. Although modern medicine is not as effective in answering the question “Why do you get allergic diseases?”, fortunately, even if the allergic substance that causes the disease cannot be identified, clinical treatment is still possible and most patients can be relieved, but avoiding exposure to the allergenic substance and desensitization are not possible.