Let them eat dirt.
New Englanders have very bad memories. That’s the only explanation for why anyone lives here. Every year in the fall people reminisce about how bad last winter was, and hope that the winter to come will be better. What these hardy souls don’t remember is that IT NEVER IS BETTER. It hasn’t been better for the entire history of New England. NPR did a bit a few days ago about how the Native Americans indigenous to this region survived winter. Turns out they did just fine, thank you, with solutions to heating and keeping warm outdoors that used natural habitat and took cues from local animals. The Europeans, having decided their way was better, froze with their wooden houses, smoky fireplaces, and inadequate wool clothing. The takeaway of the piece was that the Native Americans worked with the environment, and the Europeans tried to change the environment.
The same thing seems to be happening in the world of microbes. Population studies suggest that as infectious disease incidence goes down and socio-economic status goes up, allergic and immunological diseases become more prevalent. This is what us medicine folks call “The Hygiene Hypothesis”. Here’s how the FDA puts it: “This hypothesis suggests that the critical post-natal period of immune response is derailed by the extremely clean household environments often found in the developed world. In other words, the young child’s environment can be ‘too clean’ to pose an effective challenge to a maturing immune system.”
In other words, we have changed the environment. Unlike the Europeans and New England winters, we have been very effective in changing it. Now, most of this has been to the good, of course. Antibiotics and vaccinations, clean water and sewage systems have vastly improved the chances of health and survival for children. However, in areas of the world in which health and hygiene measures have lagged, infectious disease rates are higher but allergic conditions are more rare. An excellent review of the hygiene hypothesis can be found in the journal Clinical and Experimental Immunology (H Okada, C Kuhn, H Feillet, and J-F Bach. Clin Exp Immunol. 2010 Apr; 160(1): 1–9)