When you traveled you got into contact with allergens that your body hadn't encountered before. If you had been in contact with those allergens when growing up then perhaps you wouldn't have had an allergic reaction?
>I found that one accepted train of thought now is that people are prone to develop allergies at any age
If you've never had soy before then how could you know whether you have a soy allergy or not?
I'm not trying to convince you either way. Just some holes in the argument.
I'm allergic to grass pollen myself. I have no idea how that squares with the argument, because I certainly never shied away from grass in the summer. But it's a fairly weak allergy.
Put in other terms, your body can overreact any time for any reason causing inflammation.
and then I travelled to another country with different kinds of pollen in the air and I wound up suffering from allergies there, how humiliating! so I thought, but really just humbling
looking up how to remedy it I found that one accepted train of thought now is that people are prone to develop allergies at any age, let alone being exposed to things different than where you grew up
so I would nip the over-sterilization argument right there. keep indoors clean, go outside.