this is a heterogeneous protein allergy. That's because normal people's intestinal digestive juice contains a variety of digestive enzymes, such as protease and peptidase. The heterogeneous proteins of water fish are digested into peptides by protease first, and then into amino acids by peptidase. The protein molecules change from large to small, and the structure changes from complex to simple, and finally they are absorbed into the blood as nutritional components. However, some people's intestinal digestive juice lacks some proteases or some peptidases, so they can't fully digest foreign proteins. In addition, these people often lack an antibody called secretory immunoglobulin A(SIgA) in their intestines, which is distributed on the mucosal surface. Normal people's intestinal mucosal surface is protected by SIgA, which makes it difficult for bacteria in the intestines to stand and reproduce on the intestinal mucosa. However, people who lack SIgA can't protect the intestinal mucosa, and bacteria in the intestines can grow and reproduce on the intestinal mucosa, which makes the intestinal mucosa inflammatory and increases the permeability of blood vessels. These undigested foreign proteins and peptides can be absorbed into the blood as antigen substances, and the human body can produce antibodies against these antigens, which are adsorbed on the surface of some cells to sensitize them. When eating the same seafood food again, these sensitized cells can release bioactive substances such as histamine, leukotrienes and so on, resulting in allergic symptoms.