Because it has become relevant in recent conversation, I'd like to do a thread on allergies and the process we use to test for them, as well as a brief primer on what gluten intolerance really is. Gather round, wee kiddies! To start, what is an allergy? Simply, it's an immune response to a substance, or allergen. There are different kinds of allergies, from environmental (hay fever, pet dander, mold, etc) to irritants (poison oak, bee stings, spider bites) to internal (food allergies.)