I think it’s parents being so paranoid of germs, they literally make their kids grow up in a “plastic bubble” so their immune systems never totally develop.
There’s truth to that.
Exposure to bacteria at a young age trains the immune system.
Studies have shown that country kids have fewer allergies than city kids, that the youngest in a family has fewer than the oldest, and that dairy farm kids, who usually drink well water, raw milk, and play about the not so clean barnyard, have the fewest of all.
In addition to that, you have a certain percentage that don't have a physical allergy to certain things, it's a mental allergy.
It has become a popular 'thing' to have an 'allergy' to certain foods/pets/etc. just so they can impose their 'will' on others.
The same people who are allergic to 'everything' on the pop list also seem to be the same ones that insist their emotional support pig be allowed to ride in the cabin on airliners. Somehow they are never 'allergic' to their own pets.