From the immunological point of view, “allergic” people often have the following characteristics: 1. Immunoglobulin E (IgE) is an antibody that mediates allergic reactions, and the amount of IgE in the serum of normal people is very small, while the serum IgE of some “allergic” people is higher than normal people 1.000 times to 10.000 times higher than normal. 2, normal people have a certain ratio of helper T-cell 1 (Th1) and helper T-cell 2 (Th2) cells, which are coordinated to keep the body’s immunity in balance. Th2 cells can secrete a substance called interleukin-4 (IL-4), which can induce IgE synthesis and increase the serum IgE level. 3, the normal human gastrointestinal tract has a variety of digestive enzymes, so that the protein food entering the gastrointestinal tract is completely decomposed and then absorbed into the blood, while some “allergic” people lack digestive enzymes, so that the protein is not fully decomposed and absorbed into the blood, so that foreign proteins enter the body to cause gastrointestinal allergic reactions. Such patients often lack the protective antibodies – secretory immunoglobulin A (sIgA), which are distributed on the surface of the intestinal mucosa, and the lack of such antibodies can cause inflammation of intestinal bacteria on the mucosal surface, which accelerates the absorption of foreign proteins by the intestinal mucosa and induces gastrointestinal allergic reactions. 4, the normal human body contains a certain amount of histamine enzyme, which has a destructive effect on the histamine released by certain cells in allergic reactions (which can cause smooth muscle contraction, capillary dilation, increased permeability, etc.). Therefore, even if normal people have allergic reactions to certain substances, the symptoms are not obvious, but some “allergic” people lack histamine enzymes and cannot destroy the histamine that triggers allergic reactions, and show obvious allergic symptoms. The underlying cause of these immunological abnormalities is often closely related to genetics.