At a core level, we have created a mismatch between our immune system—one of the longest surviving and most refined balancing acts in the world—and our environment. Thanks to all the powerful learning we’ve done as a species, our immune system isn’t getting the regular interaction with germs that helped to teach and hone it—that “trained” it. It doesn’t encounter as many bugs when we are babies. This is not just because our homes are cleaner, but also because our families are smaller (fewer older kids to bring home the germs), our foods and water cleaner, our milk sterilized, and on and on.
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