What is an allergic reaction? An allergic reaction, also known as a metamorphosis, is an abnormal reaction of the body to one or more substances that are generally harmless to normal people. It is mainly caused by an excess of a special antibody called immunoglobulin E (IgE) in the body of the allergic person. It reacts with allergenic substances (allergens) in the environment and stimulates the body to release excessive amounts of chemicals, which in turn produce various allergic symptoms. What is an allergen? Allergens are also known as sensitizers or allergens. Allergens are colloquial terms, while sensitizers or allergens are medical terms that refer to antigens that can cause allergies. Their common feature is that the body is sensitized after a certain period of exposure to the allergen. The duration of the sensitization period can be long or short, and there are no clinical symptoms during this period, and the allergic reaction can only occur when the allergen is re-exposed. Therefore, the first exposure to the substance will not be allergic, and the symptoms of allergy will occur only after repeated exposure. After repeated exposure, the symptoms will generally get progressively worse. Therefore, in order to eradicate allergies, you should first find the allergen and avoid contact in order to avoid recurrence.