Allergies and the Hygiene Hypothesis
The hygiene hypothesis says that being too clean can produce unintended effects, such as a greater incidence of allergies and asthma among children. Is this really true?
Let’s dig into the science of the hygiene hypothesis, along with the latest research on the topic.
Dirt contact and diversity
In a 2018 study, researchers from the University of Helsinki tested volunteers with skin swabs and microbiological testing. They took skin swabs before and after contact with various biological materials. These included contact with the soil. And contact with plant materials. They also tested clean hands.
The researchers found that contact with soil and plant materials created the most diversity of bacteria on the skin. These included healthy bacteria such as Actinobacteria, Bacteroidetes and Proteobacteria. Greater diversity of these sorts of bacteria help protect the skin against a variety of viruses and bacteria infections. We can see this with the following study.
Early life exposure and allergies
In another 2018 study, researchers from Wake Forest University studied 248 newborn babies from the hospital. They tested the babies for their risk of contacting eosinophilic esophagitis in relation to whether they breastfed and cross-referenced their genetic susceptibility to eosinophilic esophagitis.
The researchers found that those infants that breastfed had a 92% decreased risk of eosinophilic esophagitis, even though they carried the higher genetic risk for the disease.
Why such a difference? Because breastfeeding exposed the infants to a greater diversity of bacteria.
This diversity expands to environmental factors as well. Wake Forest and University of North Carolina School of Medicine scientists expanded the early life exposures to antibiotic use, cesarean delivery, acid suppression and other environmental factors. Yes, they found that using antibiotics actually increased the risk of contracting infections and allergies later on. And they found that greater exposures decreased the risk of disease among infants.
This of course extends to adults too.
Hygiene hypothesis tested
A few years ago, Swiss, German and U.S. researchers conducted a large study comparing Swiss children who lived on farms with Swiss children not living on farms. The study showed that the Swiss children who lived on farms had significantly less incidence of allergies and asthma than did the Swiss children not living on farms.
In that Swiss study, nearly 14,000 children were surveyed between 2006 and 2007, including over 3,000 farming children and almost 11,000 non-farming children. In this study, 38% of the non-farming children had allergies compared to 19% of the farming children, and 19% of the non-farming children had asthma compared to 15% of the farming children. In addition, 19% of the non-farming children had allergic dermatitis compared to 16% of the farming children.
The 2012 report adds data to this study, taken from a survey of Amish children living in Indiana. The results found an even lower rate of allergies and asthma among the Amish children as compared to the non-farming Swiss children. Here 157 children were surveyed, and only 5% had asthma compared to 19% in Swiss non-farming children, while 6.4% had skin allergies compared to 19% in the Swiss non-farming children. In addition, 15.4% of the Amish children had hay fever compared to 38% of the non-farming children.
The national broadcast media reports, together with interviews of conventional medical doctors interpreted the results as relating to exposure to germs on the farm. The farming children, they assumed, have more exposure to germs than those not living on farms. This is combined with the fact that the farming children also tended to have more siblings, which is also attributed to more germ exposure.
NBC interviewed two immunologists that mirrored this interpretation. Dr. Samuel Friedlander with the University Hospitals Case Medical Center in Cleveland told NBC that, “I believe that the immune system is like an army. So, if the army doesn’t have something to fight like microbes, it’s going to fight things like allergens in many cases. People [who] live on farms are exposed to more microbes and as a result the immune system tries to fight those bugs and then, in turn, the body doesn’t have to fight allergens.”
University of California San Diego’s Dr. Richard Gallo, carried this over to hand sanitizers. “It’s a change in your allergic set point. So being too clean can lead you to have a high allergic set point that will overreact to the environment,” he told NBC.
While the concept of greater exposure certainly has merit, it does not provide certainty, and largely misses the bigger picture. In fact, it could be said that the non-farming Swiss children – who lived in areas with greater human populations than the farming children – were likely exposed to more germs simply because they had more exposure to a greater number of people. Living in more populated areas, they were exposed to more crowding in the form of schools, transportation, entertainment and social activities. While farm children may have more animal exposure than non-farm children, this does not mean they necessarily had more contact with germs.
The hygiene hypothesis and germ exposure
The hygiene hypothesis alone has also been contradicted by some research showing that poorer metropolitan families in different countries have greater incidence of allergies and asthma, even though those poorer families had more siblings and greater exposure to germs due to less sanitary conditions. Thus, relying upon the hygiene hypothesis alone to explain this farming versus non-farming result is short-sighted.
In other words, none of these studies took any bacteria exposure counts. The conventional interpretations are simply assuming the farming children have more germ exposure. What they are missing is the fact that during disease outbreaks, those living in cities will contract greater levels of the disease due to the increased exposure to germs being passed from one person to another. A person living on a farm is more isolated from this greater level of pathogenic germ exposure.
The researchers themselves admitted this short-sightedness. “Previous studies in Switzerland and Crete show a protective effect of farm life or rural living, with a 50% reduction in the prevalence of allergic sensitization as compared with nonfarm or urban living. Therefore, given the exceedingly low level of sensitization of 7.2% among Amish children, we feel that there may be additional protective factors in this population.”
The dietary difference
The more clear distinction between the farming children of both the Amish and the Swiss children lies within the type of germ exposure, and more importantly, their diets and lifestyles. Importantly, both the Swiss farm and the Amish children drank significantly greater amounts of raw milk and raw milk derivatives in the form of fermented dairy such as cheese and cottage cheese.
These foods all contain generous quantities of probiotics. The study results show that between 79.5 and 87 percent of the farming children from both studies drank raw farm milk, as opposed to none of the non-farming Swiss children.
This is consistent with many other studies that have shown that probiotic supplementation results in fewer allergies and asthma.
There are a variety of reasons that probiotics boost immune response and help prevent allergies and asthma among children, and breast-feeding (another “raw milk” source of probiotics) results in fewer allergies, wheezing and asthma.
Other research finds that antioxidants reduce allergies in kids.
What kinds of germs?
While the hygiene hypothesis may have a role to play, the hygiene hypothesis does not differentiate between the kinds of germs being exposed to. This is despite the fact that hundreds of other studies have proven that it is the kind of germ we are exposed to that matters. Some germs are pathogenic and some germs are probiotic, while still others are eubiotic.
Farm-living bolsters the probiotic conclusion even without raw and fermented dairy because children who play outside in the dirt will pick up soil-based organisms that grow into probiotic colonies within the gut. Having less exposure to outdoor recreation will thus certainly lead to fewer probiotic colonies within the gut among children.
The findings are clear: Children who consume more probiotics in the form of raw milk, playing outside more often and breastfeeding have less allergies and asthma.
This isn’t saying that the overuse of hand sanitizers is also not an issue to consider. Hand sanitizers remove more than just the bad germs: They also remove the good germs from our hands – and these good germs are called – you guessed it – probiotics.
Grönroos M, Parajuli A, Laitinen OH, Roslund MI, Vari HK, Hyöty H, Puhakka R, Sinkkonen A. Short-term direct contact with soil and plant materials leads to an immediate increase in diversity of skin microbiota. Microbiologyopen. 2018 May 29:e00645. doi: 10.1002/mbo3.645.
Jensen ET, Dellon ES. Environmental factors and eosinophilic esophagitis. J Allergy Clin Immunol. 2018 May 2. pii: S0091-6749(18)30627-4. doi:10.1016/j.jaci.2018.04.015.
Jensen ET, Kuhl JT, Martin LJ, Langefeld CD, Dellon ES, Rothenberg ME. Early-life environmental exposures interact with genetic susceptibility variants in pediatric patients with eosinophilic esophagitis. J Allergy Clin Immunol. 2018 Feb;141(2):632-637.e5. doi: 10.1016/j.jaci.2017.07.010.
Holbreich M, Genuneit J, Weber J, Braun-Fahrländer C, Waser M, von Mutius E. Amish children living in northern Indiana have a very low prevalence of allergic sensitization. J Allergy Clin Immunol. 2012 Jun;129(6):1671-3.
von Mutius E, Vercelli D. Farm living: effects on childhood asthma and allergy. Nat Rev Immunol. 2010;10:861–868
Adams C. Asthma Solved Naturally: The Surprising Underlying Causes and Hundreds of Natural Strategies to Beat Asthma. Logical Books, 2011.
Adams C. Hay Fever and Allergies: Discovering the Real Culprits and Natural Solutions for Reversing Allergic Rhinitis. Logical Books, 2012