The Hygiene Hypothesis: Exploring the Connection Between Allergies and an Agrarian Lifestyle

Here's a look at the latest science on what leads to a healthy immune system.

| March/April 2013

  • Studies have shown that children who grow up on farms have fewer allergies than those who don't.
    Photo By Veer
  • Unlike many medical disorders, rates of allergic disease increase as education and income levels rise.
    Photo By Veer
  • Farms are richer in microbial environments than most modern dwellings—as are homes with pets or many young children.
    Photo By iStock
  • In 2001, one out of 14 people in the United States had asthma. By 2009, it had increased to one in 12.
    Photo By Shutterstock
  • "The sort of environment we evolved in much more resembles a Bavarian cowshed than it does a modern apartment in New York or San Francisco." —Moises Vala squez-Manoff
    Photo By Laurel Kallenbach

Whether we’re aware of it or not, many of us are living with immune systems that are slightly out of whack—and, incidentally, making us feel miserable. Take allergies, for example. If you’re an allergy sufferer, you have a lot of company. Maybe it’s pollen that makes your nose twitch, or maybe you—or your child—have a nut allergy that threatens to send you to the emergency room if you accidentally eat something that contains the slightest trace of peanuts. An allergy is the product of an overactive immune system—the body’s natural defenses against infection mobilized against harmless foreign particles.

Asthma is another form of allergic disease, and has its own serious consequences. Like allergies, it often develops in childhood and can be treated, but not cured. And then there are autoimmune diseases—less common but often more debilitating than allergic diseases—including conditions such as lupus and multiple sclerosis. These diseases are caused when the immune system starts attacking the body itself.

Both allergic and autoimmune diseases are on the rise in the United States, and researchers have been working to understand why. In fact, there’s a pretty solid theory about what’s going on. It’s called the “hygiene hypothesis,” and it helps explain a curious fact that has been documented by recent research: You’re less likely to develop allergies and asthma if you grow up on a farm.

Documenting The Farm Effect

I started my research by calling Mark Holbreich, an allergist who has worked in Indiana since 1987. Both he and his wife are physicians, and several years ago, they began to treat people within the local Amish community, many of whom did not have easy access to medical care. But Holbreich quickly realized there was relatively little need for his services among the Amish. They had surprisingly low rates of allergy—even many of the people who came to him for treatment turned out to have other conditions, not allergic diseases.

As it turned out, a similar phenomenon had already been documented in Europe. “Around 2002, the first literature appeared in a German study that coined the term ‘the farm effect,’” Holbreich says. The researchers were looking at asthma and allergy rates among farming families, and found that those who worked in barns around large livestock were less likely to have these conditions. “When that article came out, I said, ‘Gee, that sounds like the Amish.’ And in 2010, I began a collaboration with German researchers,” Holbreich says. The resulting article was published in 2012 in the Journal of Allergy and Clinical Immunology.

The European study subjects lived in rural parts of Switzerland, and the Amish community in Indiana was living a similar agrarian lifestyle. “We decided to do a study looking at how common allergies were in these children,” Holbreich says. “We weren’t looking necessarily for illness, but for a positive skin test, what we call allergic sensitization.” If you test children in the general population for allergies, about 50 percent will have at least one positive skin test. “In the Swiss farm children, it was about 25 percent; in the Amish children, it was about 7 percent,” Holbreich says. That’s a huge difference—so now the question was, why?

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