Just came across this fascinating article at sciencefocus.com opening the debate about how clean is healthy? I've always wondered if we need a little dirt to teach our immune system what's good and what's bad for us. They go a step further and say that our immune system needs bad stuff otherwise it might start attacking the good stuff within us.
That completely turns the argument on its head.
“The micro-organisms that we evolved with, long before we began this modern lifestyle, became a crucial part of our physiology,” says Rook. “In this state of ‘evolved dependency’, these microbes took the role of switching on the regulatory pathways that allow our immune systems to function as they should. Without exposure to these microbes, our immune system attacks otherwise harmless foreign molecules.” Rook has labelled this new hypothesis the ‘old friends mechanism’; others call it the ‘microbial exposure theory’.