While spring flowers make people happy, some people suffer from coughs, runny noses, asthma and itching all day long. The disease they suffer from is pollen allergy. Why do we have allergies? Besides pollen allergy, we often see some other allergic reaction symptoms in our life. For example, some people who eat fish or shrimp quickly become nauseous, vomit, and itchy, which are food allergies. Likewise, there are also people who will have allergic reactions to chemical fiber clothes, detergents, oil dyes, cosmetics, etc. Allergy is an abnormal reaction of the body’s immune system to a substance that is not harmful in itself, also known as a metamorphosis. The body’s immune system acts as an antigen to foreign substances to produce antibodies or other chemicals to protect the body from the foreign substances. In general, the immune system can ignore harmless substances, such as food, and react defensively only to harmful substances, such as bacteria. If the body’s immune system cannot distinguish between harmful and harmless substances, but attacks harmless substances as it does harmful substances, then the body will have an allergic reaction. The substances that stimulate allergic reactions are allergens, such as pollen, fish and shrimp, penicillin, etc. Although allergens are diverse, they act on the body through the following channels: (1) Ingestion: Allergies caused by foods such as milk, fish and shrimp. (2) Inhalation: such as mold, pollen, dust mites and other allergies caused through the respiratory tract. (3) Contact: such as allergy caused by cosmetics, paints, nickel-plated products, etc. (4) Injection: such as allergy caused by penicillin, etc. Who is prone to allergy? Although allergic reactions are common in life, not everyone is allergic. Allergies are related to heredity, so allergic diseases are also called somatic diseases. Nowadays, the complexity of the external environment, such as the structure of food, the texture of the clothes worn, and the sources of pollution in the water and air, can lead to an increase in the number of allergic patients. How to prevent and treat allergic reactions? The key to preventing allergic reactions is to find out what you are allergic to, that is, to find out the allergen, and then to target prevention, which can generally be done in these ways: (1) Avoid: If you are allergic to crab, don’t eat it; if you are allergic to pollen, avoid outdoor activities or go to places where there is no such pollen. (2) Avoid: If one is allergic to penicillin, do not use penicillin. (3) Substitute: If you are allergic to milk then you can substitute fermented milk products. (4) Move: Remove the things that cause allergies, they may be your favorite magnolia flowers or camphor wood boxes. The most basic medication for treating allergies is an antihistamine, and the most convenient and quickest medication is an aerosol. It works quickly, but it is a superficial treatment that does not treat the root cause. The treatment that really targets the cause is immunotherapy also known as desensitization. It requires the doctor to find the exact allergen of the patient, then collect it and make a medicine. The allergic person is exposed repeatedly, from little to much, so that the body gradually adapts to the substance.