Gisela Telis writes for the Washington Post that, “A growing body of evidence suggests that all the antibacterial-wiping, germ-killing cleanliness of the developed world may actually be making us more prone to getting sick– and that a little more dirt might help us stay healthier in the long run.”
The idea, known as the hygiene hypothesis, was first proposed in 1989 by epidemiologist David P. Strachen, who analyzed data from 17,414 British children and found that those who had grown up with more siblings (and presumably more germs) were less likely to have allergies and eczema. Since then, the theory has been cited as a possible explanation for everything from multiple sclerosis to hay fever and autism. But its particulars aren’t so clean and clear.
Here’s what researchers do know: Our immune systems need bugs. They rely on early encounters with germs to learn how to protect our bodies.
“Bacteria, fungi, lots of these things we think of as bad — they’re all part of our environment, and we evolved to live with them,” says Michael Zasloff, an immunologist and physician at Georgetown University Medical Center. Through exposure to these microbes early in life, your immune system learns what’s harmful and what isn’t, he says, and that readies the immune responses you’ll have for the rest of your life.
“The body has got to know friend from foe,” Zasloff says. If your body learns that a specific microbe or substance — any antigen, or visitor to the body — is a foe, it will send immune system cells to destroy it. If it recognizes the antigen as a friend, the immune system will leave it alone. “Exposure tells the immune system, ‘These are the things you’re going to run into all the time, so you don’t need to worry about them.’ ”
According to the hygiene hypothesis, bad things can happen if this early exposure doesn’t take place or if it doesn’t include the right microbes. The immune system can become overly sensitive, overreacting to non-threats such as pollen or dander as if they’re potentially harmful. When combined with certain genetic traits, this process can lead to conditions such as asthma and allergies, says Kathleen Barnes, an immunogeneticist at Johns Hopkins University who specializes in the genetics of asthma.
Barnes’s work has revealed that although genes play a key role in the development of asthma, changing a population’s exposure to microbes — by protecting them from parasitic diseases, for example — can make asthma rates rise. That suggests that hygiene may also play a role in asthma.
Telis also sites a, “2012 study of Amish and Swiss farm and non-farm children,” that found much lower rates of, “Asthma, hay-fever and eczema,” in the farm-dwelling children.
The farm dwellers differed from their non-farm peers in several ways: They had more exposure to livestock and the microbes that come with them; they were more likely to drink raw milk, which contains microbes not found in pasteurized milk; and they tended to have more siblings at home.
Because each of these factors has been associated with reduced risk of allergies and related diseases, researchers can’t pinpoint which factor or combination of factors provides the protection.
A 2007 study of Russian and Finnish children is also sited for this article and once again, the children raised in more rural areas fared better.
I read an article in Smithsonian Magazine that shed further light on the Finnish study conducted by physician and researcher Mikael Knip. Written by Andrew Curry, the article is titled, “The unintended (and deadly) consequences of living in the industrialized world.”