My question involves release of Histamine from mast cells in the body during an allergic reaction. I understand the process if IgA and the mast cells phagocytize's the deaminated histadine.

But what exactly is the purpose of this histamine release? I know the histamine causes puffy eyes, sneezing, all the classic allergic responses. I always thought immunoglobulins were supposed to fight allergens in the body. But whats the deal with histamine? How is it beneficial to the allergic response? All it does is seem to cause problems, but obviously its there for a reason.