As discussed in Chap. 7 of the book, the hygiene hypothesis suggests that reduced exposure to dirt during infancy in Western developed countries leads to increases in allergies, eczema, and possibly auto-immune disease. It is clear that these countries are facing an epidemic of allergies and even potentially lethal food allergies. It is also true that animal experiments have shown that early exposure to microbes “educates” the immune system such that it does not over-react to new stimulants, as well as microbes normally living the gut (“commensal” bacteria). The Nov. 24 issue of Nature has an up to date commentary on the hygiene hypothesis and allergies, as well as a story about attempts to use commensal bacteria such as those commonly found in yogurtto combat allergies. The bottom line is that the results of such studies are mixed at this point, but investigators remain optimistic that the right combination of commensals, genes and lifestyle may result in an effective therapy.
The story contains several quotes from my colleague Sarkis Mazmanian, who is also cited in my book, as we are collaborating on a project on commensal bacteria in the mouse model of the autism risk factor, maternal infection.
Oh, and worms? Yes, using parasitic worms (helminths) to educate the immune system back into balance is also being tested in autoimmune disorders of several types.