However, in some people, those of us who are prone to allergies, our immune system responds to harmful things, but also things that are relatively harmless, and generally cause no reaction in
people who do not have allergies. In
allergies, our body is fighting itself, and this is bad.
These harmless things that cause allergies are called allergens. Some common allergens are pollens released from trees, mold, hay, grass, dander, and food.