Hypersensitivity generally refers to a hypersensitivity reaction, an abnormal immune response, which simply means that the body’s defense cells overreact to an antigen, also known as an allergic reaction. Hypersensitivity reactions generally lead to a number of diseases. Some common ones are autoimmune hemolysis, systemic lupus erythematosus, and other rheumatic and rheumatoid diseases, all of which are hypersensitive reactions, and all of which are abnormal pathological conditions. In addition, there are also common clinical type I hypersensitivity reactions, such as drug anaphylaxis, allergic rhinitis, allergic asthma, urticaria and so on. Hypersensitivity reactions are clinically difficult to treat and can be treated with immunosuppressants (methotrexate) and drugs such as glucocorticoids (prednisone) and loratadine. Diagnosis and treatment of specific diseases need to be carried out under the guidance of a physician.