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In fact, each and every one of us has billions of microorganisms hanging out on our skin and inside our bodies. Many of them are our friends, helping us digest things we can't otherwise digest and warding off infections.

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Incidentally, one theory as to why allergies are so prevalent these days is because chlorinated water killed off a gut parasite that hooks into the intestine and excretes an immunosuppressant. Without that suppressant action that we evolved with the "expectation" of having, we now all have more potent immune systems than "designed". The result is that it reacts to things that pose no harm, like pollen and dust mite debris.

On the other hand, dirty water has killed a lot more people than allergies have.

Whenever I reflect on this fact, I feel like something H.P. Lovecraft might have written about.

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