What sort of problem is an allergic reaction?

Let help understand?: An allergy is a hypersensitivity disorder of the immune system.[1] allergic reactions occur when a person's immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen. These reactions are acquired, predictable, and rapid. Allergy is one of four forms of hypersensitivity and is formally called type i (or immediate) hypersensitiv.

Immunologic: An allergic reaction is the body's immunologic response to a substance (typically a protein) that it determines is "foreign." the body's th2 type of t cells interacts with b cells that produce ige antibodies. When ige antibodies that are present on mast cells subsequently encounter the allergen, the mast cell releases histamine and other chemical mediators that lead to the symptoms of allergy.