1. What is an allergy An allergy is simply an allergy to a substance. When you eat, touch or inhale a substance, your body will overreact; under normal circumstances, the body will make antibodies to protect the body from disease; but the body of an allergic person will mistake a normal harmless substance for something harmful and produce antibodies, and the substance will become an “allergen”. This allergic reaction can lead to a number of diseases, such as allergic rhinitis, allergic asthma, allergic dermatitis, etc., which usually do not occur in normal people. The causes of allergy include two major aspects: intrinsic factors and extrinsic factors: intrinsic factors are having an atopic constitution, which plays a leading role in the development of allergy. Early and complete desensitization is the key to treating allergic rhinitis, allergic asthma and preventing recurrent skin allergies. There are also many external factors. They include diet, inhalants, climate, and exposure to allergenic factors. Among them, inhalation of pollen and dust mites, proteins such as eggs and milk, and exposure to chemicals, soaps and detergents are the most common causes of skin allergy. Because of such a complex etiology, and the intertwining of onset and triggering factors, skin allergies recur. 3. Common skin allergic diseases (1) Eczema. (2) Atopic dermatitis. (3) Contact dermatitis. (4) Drug rash. (5) Urticaria. (6) Anaphylactic purpura. (7) Anaphylaxis, etc. 4, common allergen detection methods (1) prick test. (2) patch test. (3) Specific IgE quantitative allergen testing. 5, the prevention and treatment of allergic diseases (1) the discovery of allergens, avoid allergens. (2) Desensitization therapy. (3) Drug intervention.