What Causes Allergic Reactions. You might blame your triggers; the pollen in the air, your best friend’s cat, for your symptoms. But actually, most of those things are harmless. What really causes allergic reactions is your immune system. It mistakes innocent things in your surroundings for a serious threat and attacks them.
An allergic reaction occurs when your body attacks a foreign substance, called an allergen. You can inhale, eat, and touch allergens that cause a reaction.
Almost anything can trigger an allergic reaction. The body’s immune system involves the white blood cells, which produce antibodies. When the body is exposed to an antigen (a foreign body such as pollen that can trigger an immune response), a complex set of reactions begins. But the disease can flare up when you’re around things that cause an allergic reaction. Your body’s immune system overreacts to substances, called allergens, that are usually not harmful. You might get hives, itching, swelling, sneezing, and a runny nose. You might have it if you have itching, redness, and peeling or flaking.