I was diagnosed with hayfever as a boy and had immunotherapy for it. It was useless. I also had frequent exposure before my diagnosis (without symptoms), which seems typical according to my doctor, because allergies tend to develop /after exposure/.
This, as my anecdotal evidence, and every medical text about it, contradicts your ideas. Please consult a doctor before doing anything you suggested to your children or yourself, because your suggestions are /dangerous/.
Dangerous as in: exposure can cause allergies that haven't been there before. Medical treatment with allergens can also cause allergies and therefore shouldn't been done willy-nilly in a prophylactic manner.
Also, suggestions like those usually bring out the quackery in people, with things like "Oh, hayfever? Let's cure it by doing summer holidays on the farm!" and "Oh, peanut allergy? I have a sandwich for you, kid!".
Clearly you have never seen proper immunotherapy (which has been in practice for decades). All patients are prescribed an epi-pen prior to starting treatment. It used to be that all doses were monitored for anaphylactic reactions but that is now clinic-dependent.
I'm not suggesting that anyone should do anything without the advice of a doctor. Yes, deliberately exposing yourself to things you are allergic to is dangerous and an allergist's guidance is very important for safety. I'm sorry immunotherapy didn't work for you but your anecdotal evidence doesn't invalidate all the published research.
Yes, allergies always develop after exposure. But not all exposure is created equal! Some types of exposure tend to cause allergies while other types tend to protect against allergies. Immunotherapy is the right type of exposure, under the guidance of an allergist.
Well, you suggested prophylactic exposure in early childhood (which is usually before any allergy is diagnosed and usually also before it is manifest):
> I suspect that in twenty years it will be standard to start infants on sublingual immunotherapy for all the common allergens (literally putting a tiny, strictly controlled amount of the allergens under the tongue once a day, simple as that) as a prophylactic
Also, even therapeuthic or diagnostic exposure can cause allergies, there is no safe exposure. Just safer and less safe.
I'm not suggesting that people do that today. I'm suggesting that it's likely where we're headed. But as I said, we need more research to get there. Prophylactic exposure in early childhood is already proven effective and strongly recommended for peanut.
This, as my anecdotal evidence, and every medical text about it, contradicts your ideas. Please consult a doctor before doing anything you suggested to your children or yourself, because your suggestions are /dangerous/.