Allergy or intolerance, revisited in excruciating detail:

I posted about this last week, and I gave you all what I saw as a clear and articulate breakdown of the difference between an allergy and an intolerance.

Interestingly, while that’s the difference as I’ve seen it in most things I’ve read that are meant for the general public, the science behind this is . . . lively.

This is insanely technical, in a way that I am not entirely qualified to explain, but has to do with what kind of antibodies are being generated.

If we think of this in terms of the allergies we’re most familiar with, human seasonal allergies, you know that the fastest solution is to take an antihistamine tablet. The histamine reaction that you are suppressing is triggered by (treating this very simplistically. If you are a biochemist or some such PLEASE let me ask you a zillion questions about histamine; I am desperately curious.) one particular antibody, called Immunoglobulin E. But there are other immunoglobulins that can be inappropriately sent out, aside from just E. (G, M, and A.)

Some research says that only the reaction of IgE/histamine is an allergy. Other reactions, by that definition, are just “sensitivities.” Another, broader, definition is that any immune response to a non-threat is an allergy.

The European Academy of Allergy and Clinical Immunology classifies the IgE response as an allergy: “The antibody type, that may cause an allergic reaction, is called IgE.” But, just in case you thought that cleared something up, they also go on to say that “Although IgE is normally involved in allergic reactions, the immune system is very complex and other immune pathways can sometimes be involved. Examples of non-IgE mediated food allergies are gluten intolerance (Coeliac disease) and systemic allergic contact dermatitis.”

If we go back to our lactose intolerance example, that is purely a lack of digestive enzyme. Physically, your body can’t break down the lactose, so you get really uncomfortable until your body can get rid of it. There is no immune response at all, histamine or otherwise.

What it looks like to me right now is that there is a concrete definition for “intolerance” (your body can’t physically digest something) and a concrete definition for “allergy” (IgE reaction). Then there is something of a murky area in the middle that is defined either as a “non-IgE allergy” or just as a sensitivity. The fact that an intolerance, by definition, doesn’t produce non-digestive symptoms is probably what produced the distinction I discussed last time, that non-digestive symptoms prove allergies. But, it isn’t that simple. Non-digestive symptoms only prove that something is not an intolerance. What it is is kind of a who-knows.

The pragmatics of this are, as I mentioned last time, less than zero. Avoidance is still your only solution.

In fact, even the non-pragmatics are iffy. Traditional serum allergy tests are looking for the histamine related antibodies. IgE testing for food allergies is highly inaccurate in humans and in dogs, as shown by double-blind exposure tests. So, even if you know for sure that your dog is having a “real” allergic reaction, a test may not show it. Jean Dodds has created a new test for dogs that can theoretically test for two of the other antibodies, IgA and IgM. She believes that this can accurately diagnose food sensitivities. She pointedly separates the IgA and M reactions from allergies, which is, as I showed above, a semantic morass. I got sucked down the science rabbit hole trying to decide if her test would be useful for Silas. (I have come to no conclusion. I suspect that, putting on my realist hat, I would never trust the results enough to make much use of them. Curious hat might win anyway.)

Now, if only someone would write “The Biomechanics of Allergic Reactions, Incredibly Precise But For Non-Experts.” I’d read it.