what is the cause of the sharp rise of immune defects in the last fifty years? Well, here it may become counterintuitive because it all has to do with microbes but in a different way. It seems that to train your immune system you need to hang out with harmless friends. Your immune system needs nice playdates to learn when to be gentle and forgiving. This more nuanced version of looking at interactions with the microbes around us has been called a few different names, but the nicest one may be the “Old Friends” Hypothesis, which focuses much more on our evolution.
