We evolved to be constantly dirty, and we live in an extremely clean society. When your immune system has a lot to fight, it doesn't worry to much about dumb shit like pollen and peanuts.
I get some weird skin issues sometimes which are almost magically fixed if I visit a natural body of water... it's clearly an issue of my immune system interacting unfavorably with a microbiome which is out of whack.
Hookworms are another option; maybe two generations ago kids regularly walked barefoot in grass and was pretty common.
And infested with worms. Most allergies are caused by the antibody we evolved to fight worms (and venom) [1].
The facebook group for DIY helminth therapy is a fascinating place, let me tell you. But there are several possible species of helminths to try. It's all a bit overwhelming.
We sure aren't exposed to the same things as 4 centuries ago, but I can't imagine we're living a what anyone would call a "clean" environment.
People in the olden days got their hands dirty chopping down trees and building solid wood tables while today we keep our hands clean by buying flat-pack furniture that out-gasses formaldehyde into our homes and our lungs.
We're much dirtier than the people were a long time ago, only it's mostly on the inside. The filth in our bodies doesn't wash off with soap.
We're vastly more sterile from a germ perspective. The term "hygiene hypothesis" is apt.
So if it runs out of intruders to fight, it will attack the body itself.