There's also the "hygiene hypothesis" which states roughly that early exposure to various pathogens helps the immune system learn what is dangerous and what is

There's also the "hygiene hypothesis" which states roughly that early exposure to various pathogens helps the immune system learn what is dangerous and what is not. If you've ever visited someplace like, say, Cambodia (parts of which are underwater much of the year) you were likely impressed by the difference between their children's exposure to the elements and those of most children in the USA. https://dhvi.duke.edu/staying-home-harming-your-child’s-immune-system https://dhvi.duke.edu/staying-home-harming-your-child’s-immu...