Indoor mold combats asthma in children. OK, maybe not. But this is a really intriguing study, regardless.

Scientists measured the humidity and the number of fungus species present in a bunch of houses. A few years later they checked in to see if any children in these homes had developed asthma–an immune system disorder that renders your respiratory system hysterical.

Hey! Weird! The houses with high moisture had more breeds of fungus–and lower rates of asthma!

That’s not how it’s supposed to work.

Except that there’s more than one road to asthma and allergy.

One is overexposure: You stand a shot at freaking out your immune system by overexposure to pretty much anything. Wood dust. Flour.

The other is underexposure. The Hygiene Hypothesis holds that we evolved as dirt-sleepers, cave-nappers, mold-breathers. Our immune system evolved a process of “learning” early in life what to freak out about, and what to ignore. But in our increasingly sterile homes, young immune systems miss out on early education. A house with low moisture offers poor habitat for fungi; and low exposure to fungi may handicap a growing immune system.

It’s just one study, and a small one at that. But it supports my private concern that ever since Stachybotrys molds made headlines in the early 1990s people have developed unnecessarily hostile attitudes toward household mold. It’s not all toxic, just as not all mushrooms are poisonous.

So there’s that. But there’s also this: Perhaps it’s interactions among mold species we need to study. Perhaps humid homes support “good” molds who compete with “bad” molds. Perhaps dry conditions favor a particular bad*ss strain of mold.

We’re pretty innocent regarding the mold kingdom. But it seems clear to me that damp, dirt floors were the standard in human shelter until quite recently; and that the lack of them is more likely what plagues us.