this has long been known. the health and diversity of your intestinal flora has a large impact on your immune system

the way to raise healthy children w/ strong immune systems is to let them eat dirt, not to wash their hands incessantly

that does harm https://www.sciencealert.com/daycares-in-finland-built-a-backyard-forest-and-it-changed-children-s-immune-systems

there is quite a lot of evidence to support the hygiene hypothesis: that having too clean an environment leads to mis-calibrated and less effective immune systems in children, ironically some of it from UW, home of arch karens IHME and carl b. https://rightasrain.uwmedicine.org/well/health/hygiene-hypothesis#:~:text=%20What%20is%20the%20hygiene%20hypothesis%3F%20%201,we%E2%80%99re%20better%20able%20to%20detect%20and...%20More%20

it's important to note that this evidence is associational and correlation based, but that there is also good understanding of the pathway by which this occurs, so it's not some shot in the dark.

US kids are getting WAY more allergies, asthma, and autoimmune disease.

when i was a kid, serious food allergies were rare.

now every class has a couple of kids and schools treat peanuts like they are polonium.

clearly, something is going on and it appears to be coming from the gut biome.

the sonnenburg lab at stanford has been a global leader on this research and it's excellent.

gut biome health and biodiversity is a key factor in healthy immune systems and generally happiness (it's linked to sertonin production)

the data is solid. https://scopeblog.stanford.edu/2015/04/28/getting-to-the-good-gut-how-to-go-about-it/

i recommend their book "the good gut" highly.

this is their tried and true advice for children.

note that it sounds almost nothing like the utter nonsense coming out of health agencies and schools right now...