Antigens that induce allergic reactions are called allergens. There are hundreds of antigenic substances that cause allergic reactions, and they sensitize the body through inhalation, ingestion, injection or contact. Common allergens are introduced as follows: A. Inhalation allergens such as: pollen, willow, dust, mites, animal dander, oil smoke, paint, car exhaust, gas, cigarettes, etc. B. Ingested allergens such as: milk, eggs, fish and shrimp, beef and mutton, seafood, animal fat, allogeneic proteins, alcohol, drugs, antibacterial agents, anti-inflammatory drugs, fragrance oils, flavors, onions, ginger, garlic, and some vegetables, fruits, etc. C, contact allergens such as: cold air, hot air, ultraviolet light, amplitude, cosmetics, shampoo, detergent, hair dye, soap, chemical fiber products, plastic, metal jewelry (watches, necklaces, rings, earrings), bacteria, mold, viruses, parasites, etc. D, injectable allergens such as: penicillin, streptomycin, heterologous serum, etc. E, mental tension, work stress, microbial infection, ionizing radiation, burns and other biological and physicochemical factors that change the structure or composition of their own tissue antigens, as well as their own hidden antigens released due to trauma or infection, can also become allergens.