How do allergies develop?
When and if allergies develop is different for each person. Many different factors contribute to whether someone develops an allergy or has allergic reactions, such as their genetics, environment, and exposure to allergens.
An allergic response occurs when your immune system makes antibodies to something that is otherwise harmless. Antibodies are proteins made by cells of the immune system to fight off substances which the body marks as foreign. Typically, we think of antibodies as helping us to fight off pathogens, such as bacteria or viruses. But sometimes antibodies are made for pollen, pet dander, or mold, which leads to allergies.
Allergic reactions occur when you are exposed to an allergen. In response, special cells of your immune system, called B cells make an antibody called IgE. This antibody responds to the allergen and leads to an allergic reaction. This is the most common type of allergic reaction that people think of and is called type one hypersensitivity.
Why is my allergic reaction bigger the second time?
Sometimes the first exposure to an allergen will not be as bad or as powerful as later exposures. This is because the first time the immune system sees something, it’s considered priming, or the primary exposure. During primary exposure, your immune system is checking out the allergen, learning how to respond, and preparing immune cells to respond in the future.
The immune system has B cells and T cells which can remember foreign substances and how to respond to them. When exposed to an allergen, your B cells may build antibodies like IgE to respond. When your body is exposed to the allergen a second time, your B cells will already have the instructions from your first exposure. Your B cells are primed and ready to go, which allows your immune response to be more powerful the second time you encounter an allergen.