Allergic diseases are abnormal immune reactions of the body caused by allergens (allergens) that result in tissue inflammation or organ dysfunction. Allergic diseases are most commonly associated with skin, inhalation, and digestive tract involvement. Allergic diseases in a broad sense include all diseases caused by allergic reaction mechanisms, but in a narrow sense, allergic reactions often refer to rapid (type I) allergic reactions mediated by IgE. The serum allergen-specific IgE test can only detect tachyphylaxis. Allergic reactions are usually classified into four types: rapid, cytotoxic, immune complex and late. Among them, cytotoxic type and immune complex type can also degranulate mast cells or basophils through complement, and clinical manifestations similar to tachyphylaxis, but without the involvement of allergen-specific IgE, and the value of serum suspected allergen-specific IgE test is usually in the normal range. The reactions caused by type I allergic reactions include: 1. eye: allergic conjunctivitis; 2. nose: allergic rhinitis; 3. trachea and lung: allergic asthma, allergic bronchopulmonary aspergillosis, etc.; 4. digestive tract: allergic gastroenteritis; 5. skin: atopic dermatitis, allergic urticaria, allergic angioedema, allergic tachyphylaxis contact reaction, etc.; 6. severe systemic reactions: allergic syndrome. These patients all have high values of atopic IgE level tests. Pseudo-allergic reaction: It refers to clinical manifestations similar to tachyphylaxis, but the patient’s serum is negative for specific IgE of the suspected allergen. This condition is due to the fact that certain substances can directly degranulate mast cells or basophils through non-allergic mechanisms, releasing histamine and other mediators, thus causing clinical symptoms similar to those of tachyphylactic allergic reactions. These substances that cause direct degranulation of mast cells and basophils without sensitization are called histamine releasing agents. It is known that certain drugs, foods or food additives can directly stimulate mast cells and basophils to degranulate or contain substances that degranulate these cells. Autoantibodies such as anti-IgE antibodies (IgG), anti-IgE receptor antibodies, as well as complement, neuropeptides, enzymes, cytokines, and inflammatory mediators; and physical factors such as light, heat, cold, pressure, and vibration can all degranulate mast cells and produce tachyphylactic symptoms, but then allergen testing shows normal serum values of IgE specific to the suspected allergen.