Total epidermal necrosis and subepidermal macules are one of the symptoms of toxic necrotizing epidermolysis bullosa drug rash. The adverse reaction of skin and/or mucosal damage caused by drugs used for prophylaxis, diagnosis, and treatment, regardless of the route of entry into the organism, is called drug rash. It is a common condition in dermatological emergencies. Toxic epidermal necrotizing drug rash is a serious skin disease with multisystem damage. It is characterized by a large area of damage and a high mortality rate. The echinocytosis test is one of the common physical examinations used in dermatology to check whether the location of blisters and macules is within or under the epidermis. 2. Skin test Skin test is the most commonly used specific test, including patch, scratch, prick and intradermal injection. Clinically, prick and intradermal tests are most commonly used, such as negative prick test; can be rechecked by intradermal test. Atopic patients can be induced to produce specific IgE after exposure to allergens. Such antibodies adhere to IgE receptors on the surface of mast cells in the skin or submucosa, and when they meet with allergens re-entering the body to form a bridge of one allergen and two IgE antibodies, a series of biochemical processes occur in the mast cells, releasing allergic mediators and producing localized wind masses, redness or itching in the skin. 3, skin smear microscopy Skin smear microscopy is a test for the presence of bacteria in blood, urine, cerebrospinal fluid, pleural fluid, pericardial fluid and peritoneal fluid. It can diagnose skin diseases caused by streptococcus, staphylococcus, anthrax bacillus, leprosy bacillus, tuberculosis bacillus, various fungal infections, amoeba, black fever, filariasis, scabies, mites, etc. 4.Physical examination of dermatological diseases Physical examination of dermatological diseases is the physical examination of the skin, such as skin scratch test, slide pressure diagnosis method, etc. Patients with positive skin scratch test often have localized itching of wind masses on tight belts, watchbands, garters, etc., and more wind masses are produced due to scratching. It is generally theorized that the skin scratching phenomenon occurs due to the involvement of IgE antibodies and is also associated with the presence of some functional abnormality of skin mast cells.