Lowry and his team are quick to caution their work hasnt confirmed any link between hygiene and mental health, at least not yet. But given that more and more families are moving into cities, though, they believe their research could have some pretty huge implications.

Its potentially alarming, for several reasons, he said. Theres a massive increase worldwide in urbanization, and by 2050, two-thirds of the worlds population is expected to live in cities. So were gradually shifting towards an existence that creates a mismatch between our evolutionary past and co-evolved relationship with things like microorganisms.

One thing we can anticipate is that we will somehow have to compensate for that lack of exposure, especially during development, to these microorganisms, Lowry added. And the strategy for doing that is not quite clear... hopefully we can resolve that over time.

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