Allergies are likely a byproduct of the immune reaction to parasites. They begin with mast cells that attach antibodies to their exteriors, and when one attach

Allergies are likely a byproduct of the immune reaction to parasites. They begin with mast cells that attach antibodies to their exteriors, and when one attaches to something it recognizes, the mast cell releases histamine and other signals to begin inflammation. This can be enough to clear parasites that have not evolved to address these effects. These parasites are now rare in the developed world, and the mast cell would likely be better disabled. I read several years ago that work was being done on a method to remove the mast cells' antibodies, which would stop much of an allergic reaction.