Many people have had a bad experience with allergies. Some people will have abdominal pain, diarrhea, vomiting, or skin rash after eating fish, shrimp, crabs and other foods; Some people will sneeze and cry after inhaling pollen or dust; Some people even have shock after penicillin injection. These are well-known allergy phenomena. But why are people allergic? Human beings have a strong immune system to deal with the invasion of foreign substances. When substances are recognized as useful or harmless by the body, they are absorbed, used or discharged in harmony; When the substance is identified as harmful, the immune system of the body will immediately react to expel or eliminate it, which is the role of the body's immune response defense system. If this response is beyond the normal range, that is, when there is no difference in attack, it will trigger an allergic reaction. These substances, which are judged by the body's immune system to be heterogeneous, are called allergens. Allergen is a necessary condition for allergy. According to medical literature, there are nearly 20000 kinds of allergens and 2000-3000 kinds of common allergens. They make the body allergic through inhalation, ingestion, injection or contact. It is mainly found in environmental factors, disease factors, drug factors, diet factors, etc. Environmental factors: such as dust mites, animal fur, pollen, fungi, second-hand smoke, ozone, sulfur dioxide, nitrogen dioxide and inhalable particles, etc. can induce allergic reactions. Disease factors: such as respiratory allergic diseases, skin allergic diseases, digestive tract allergic diseases, eye allergic diseases, systemic allergic diseases, etc. Drug factors: The drugs that cause drug allergy mainly include antibiotics such as penicillin, cephalosporins, aminoglycosides, sulfonamides, quinolones, etc. Dietary factors: There are more than 170 kinds of food that can cause allergies, such as milk, eggs, peanuts, nuts, shelled seafood, soybeans, wheat, etc. The above foods are related to more than 90% of food allergies. In daily life, people still have many "misunderstandings" about allergies. If allergy is mistaken for allergy, which leads to treatment deviation, take skin as an example. Skin allergy has two characteristics, one is the participation of the body's immune system, the other is atopy, which is like a lock and key. If it is not the allergen that the body thinks, it will not appear allergic; The skin sensitivity is based on the destruction of the skin barrier, or the skin becomes less tolerant due to trauma or inflammation and other reasons. It will react to various non-specific external stimuli, such as cold and hot, rubbing, acid and alkali. In addition to sensitivity, many people mistake food intolerance for allergy. In fact, there is an essential difference between the two. Food intolerance usually occurs only when the consumption is large, and the symptoms are not serious, mainly manifested as diarrhea and vomiting; Food allergy has nothing to do with food intake. A small amount of food can also cause sensitization, mainly manifested as nausea, stomach pain, accompanied by skin rash or general discomfort, even life-threatening. Therefore, it is important to learn how to identify. Allergy is an emergency. Allergies can be accompanied by sneezing, runny nose, itching, stuffy nose, wheezing, coughing, shortness of breath, chest tightness, wheezing, angioneurotic edema, itching and other symptoms. Severe cases can threaten life, so once found