Yeah. Calling bullshit on this.

I'm the 2nd oldest of 7 kids. That house was never clean. We had all kinds of pets. I would play in the woods, make mud pies, catch weird bugs, eat wild berries and onion grass. I pretty much had the "go outside and play in the dirt to build character" childhood. I've got a couple of food allergies and pet dander allergies. My oldest sibling has an auto-immune issue, the ones just after me are pretty healthy, just some minor lactose intolerance, and the two youngest (from my step dad) have a bunch of weird allergies, like potatoes and milk.

It's a genetic roll of the dice. The reason why allergies seem more common is because more kids are able to survive anaphylaxis at a young age thanks to modern medicine and quick emergency response times... Like I went through when I spontaneosly developed a severe fish allergy at 4 years old.