[dinfinity]

The actual answer is pretty much in the article and what you would expect:

"The prevalence of allergic sensitization - the development of antibodies to allergens and the first step to developing an allergy - was six times higher in the Hutterites. The researchers first ruled out a genetic cause; in fact, an analysis showed that the Amish and Hutterite children were remarkably similar in their ancestral roots. Instead, the main difference between these two populations seemed to be the amount of exposure as young children to farm animals or barns.

“The Hutterite kids and pregnant moms don’t go into the animal barns. Kids aren’t really exposed to the animal barns until they’re like 12 or so, when they start learning how to do the work on the farm,” Ober said. “The Amish kids are in and out of the cow barns all day long from an early age.”

When analyzing samples of Amish and Hutterite house dust, they found a microbial load almost seven times higher in Amish homes. Later experiments showed that the airways of mice that inhaled Amish dust had dramatically reduced asthmalike symptoms when exposed to allergens. Mice that inhaled Hutterite dust did not receive the same benefit."

[lstamour]

Good points. And it probably isn’t formaldehyde. The only thing I’ll add is that formaldehyde can inhibit or kill bacteria. And I also recently learned the hard way that limonene or other terpenes (from fruits or cleaning products or air fresheners for example) can react with ozone and produce formaldehyde even in the absence of combustion. And I’ve a strong opinion now that science and society ignores the dangers of formaldehyde and VOCs about as much as we used to ignore germs and other things we can’t usually see. Until heat pumps with fresh air exchanges are considered standard or specified by housing code, we will probably always have to deal with VOCs as we don’t have an accurate way to measure them and identity their sources except in industrial contexts. Saying this because while an open window is the cheapest way to get fresh air, it often isn’t the temperature or humidity we expect.