Thus, appendicitis is a disorder of the WEIRD world. So, too, are many allergies and autoimmune disorders, for which there is solid, and growing, evidence to support the “hygiene hypothesis.” The hygiene hypothesis posits that because we live in ever-cleaner surroundings, and are therefore exposed to ever fewer microorganisms, our immune systems are inadequately prepared, and so develop regulatory problems, such as allergies, autoimmune disorders, and perhaps even some cancers.17 Our immune systems are not functioning as they evolved to do, suggests the hygiene hypothesis, because we have
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