Baby Acrobatics: Kids Health Study

Grandparents resisting the temptation to overuse hand sanitizers after playing outside:

In 2016 Finnish researchers added forest floor, sod, and planters for growing annuals to 10 playgrounds in daycare facilities where commercial floors once stood.28 days later the kids playing in these environments had measurably different immune systems. Their skin microbiomes diversified, their T cells went up (immune systems=healthier) and signals for allergies and immunity moved in the right direction. All of these responses happened within 4 weeks with a tiny shift of their biodiversity.

The biodiversity hypothesis: Regular exposure to diverse microbes from soil, plants, and animals trains the human immune system.