The Hygiene Hypothesis -- Redefine, Rename, or Just Clean It Up?

Linda Brookes, MSc; Laurence E. Cheng, MD, PhD

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April 06, 2015

In This Article

What Is the Current Understanding of the "Hygiene Hypothesis"?

A landmark 2002 study among farming and nonfarming households in Europe[5] extended the principle of a protective effect of early-life microbial exposures beyond viruses, according to Dr Cheng. "You could see that despite genetic similarities between all of the populations, the children who grew up on farms had much lower rates of allergic diseases than their nonfarming counterparts," he recalled. The study demonstrated that allergic diseases and asthma were less likely to occur in children with high environmental exposure to endotoxin (bacterial lipopolysaccharide).

Another study out of Detroit, the Childhood Allergy Study, was able to show a similar effect in a more urban environment in the United States.[6] "Basically, having dogs and/or cats as pets protected children against allergies, and the effect was additive, so the more dogs or cats they had, the better protection they had," Dr Cheng said. He also pointed out the GABRIELA study (Multidisciplinary Study to Identify the Genetic and Environmental Causes of Asthma in the European Community [GABRIEL] Advanced Study), which was "a very nice correlative piece, in which not only could you look at the same exposures but you could actually look at the microbiome itself and see that early-life exposures also led to greater diversity of environmental microbial exposure that was correlated with less allergy, even in these urban environments."[7] "I think these are incredibly important data...but I do not think it is as simple as feeding bacteria to your kids," Dr Cheng cautioned.

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