"Allergic diseases have reached pandemic levels," begins David Artis's new paper in Nature Medicine. Artis goes on to say that, while everyone knows allergies are caused by a combination of factors involving both nature and nurture, that knowledge doesn't help us identify what is culpable—it is not at all clear exactly what is involved, or how the relevant players promote allergic responses.
There is some evidence that one of the causes lies within our guts.
Epidemiological studies have linked changes in the species present in
commensal bacteria—the trillions of microorganisms that reside in our
colon—to the development of allergic diseases. (Typically, somewhere
between 1,000 and 15,000 different bacterial species inhabit our guts.)
And immunologists know that signaling molecules produced by some immune
cells mediate allergic inflammation.
Animal studies have
provided the link between these two, showing that commensal bacteria
promote allergic inflammation. But these researchers wanted to know
more about how.
-from a post at ArsTechnica, to which Glenn Reynolds of Instapundit links.
My theory is that the high proportion of animal-based foods that we eat is a very significant contributor. Compare the link at my "Pink Slime" post, which states that the meat "leavings" are handled by gut bacteria largely and not by digestion in the stomach. Just connecting some dots here, and it may not mean anything.