The Hygiene Hypothesis: What it is and Why it Matters Today

The Hygiene Hypothesis: What it is and Why it Matters Today

We have never been more disconnected from nature. 

For centuries, our earliest ancestors existed in harmony with the natural world. They lived outside, intimately in touch with the earth and soil, eating the seasonal wild plant foods they gathered, waking and resting in sync with the sun’s rhythms.   

Through this lifestyle and diet, they were exposed to the healthy bacteria found in their environment, particularly in the soil. These bacteria played an integral role in their health and well-being, strengthening their immune system, protecting against allergic diseases, and providing a primitive yet effective way for fighting gut ailments. Early man had a short lifespan due to accidents and deadly diseases, but he may well not have suffered from many of the maladies we suffer from today.

Now, our urbanised world looks very different. We’ve all but lost this vital connection to nature and many of the benefits that come with it. Advances in medicine and science have of course led to profound gains in public health: vaccinations and antibiotics now protect us against many of the diseases which might previously have killed us. However, as we cut ourselves off from the “bad” bacteria, we do the same with the “good” kinds. 

Meanwhile, our environment has become hyper-sanitised. Food is sterile and processed. Tarmac is rapidly replacing soil. Our lifestyles are increasingly sedentary. Together, these factors have succeeded in severing our vital connection with nature’s beneficial microbes. Evidence suggests that because of this we have a much less diverse microbiome than previous generations. 

Scientists have linked the disruption in the human microbiome to a plethora of ailments and illnesses, which have only emerged in the last 50 years, ranging from irritable bowel syndrome (IBS), allergies, and food intolerances, to weakened immune systems (1,2). Our sedentary lifestyle, along with a disconnect from nature are the most likely causes for this rise.

In the rapidly developing economies of the East, things don’t look much better. A pair of cross-sectional studies performed ten years apart showed that the prevalence of food allergy in China more than doubled between 1999 and 2009, from 3.5% to 7.7% (3). Meanwhile, a 2018 study of urban school children in India showed that asthma rates nearly tripled from 2008 to 2018, from 7.59% to 18.2% (4).

Simply put, we’ve become too “clean” for our own good—a concept commonly known as the Hygiene Hypothesis. To borrow Marie Antoinette’s adage “let them eat cake”, we might say “let them eat soil!” And by ‘eat soil,’ we mean identify the key bacteria found in soil and utilise them as nature’s dietary supplement. 

The Hygiene Hypothesis

The Hygiene Hypothesis is a concept first formally proposed by British epidemiologist David Strachan in 1989. Strachan observed that the virulence of so-called “allergic diseases” such as asthma, eczema, and hay fever was reduced as a result of being infected at an early age. Larger households in which siblings were likely to infect one another, he found, conferred protection from such allergic conditions. In a way, it was the “unhygienic” conditions of larger households that conferred this vaccine-like protection from allergies (5,6). 

These observations have implications beyond the household, however. Stracham linked the rise in allergic conditions in the 20th century with an increase in “personal cleanliness” (7) and, to follow his logic, exposure to such illnesses and environmental bacteria at an early age can in fact aid in the development of their immune system.

Fast-forward to the 21st century and our obsession with cleanliness has only increased. We also understand more about the role that bacteria play in the human body. We know that the overuse of antimicrobial medicines such as antibiotics has led to the emergence and spread of drug-resistant pathogens (8), and that microbes play an active role in educating our immune system (9).

Strachan’s Hygiene Hypothesis may be dated, but the principles it establishes have never been more relevant to our daily lives. Within reason, we need to understand that there’s such a thing as too hygienic when it comes to bacteria. In our fight against “bad” bacteria, we risk also losing vital “good” bacteria that boost our immunity and nurture our microbiome.

There are two complementary ways we can address the sanitization of daily life that Strachan identified. The first is to go outside and experience the natural world first hand, especially when we’re young. This exposure to environmental bacteria and allergic conditions will boost natural immunity. The second is to take a daily probiotic that’s scientifically formulated to deliver beneficial bacteria directly to your gut, intact. This has a range of benefits, improving everything from our gut health, to skin luminosity, immune response, and even cognition.

That second solution, we think, can offer the best of both worlds—the cleanliness of modern life and the health benefits of nature’s bounty.

Want to learn more? You can read about our Functional Probiotic here.


  1. Tasnim, N., Abulizi, N., Pither, J., et al. Linking the Gut Microbial Ecosystem with the Environment: Does Gut Health Depend on Where We Live? Front Microbiol 8, 1935 (2017).
  2. Leung, A. S. Y., Wong, G. W. K., Tang, M. L. K. Food allergy in the developing world. The Journal of Allergy and Clinical Immunology 141(1), 76-78 (2018)
  3. Ibid.
  4. Gupta MK, Patodia J, Chaudhary P, Kakkar M. The rising trend of asthma prevalence in urban school children of Jaipur: A questionnaire based study. Indian J Allergy Asthma Immunol 32(1), 10-14 (2018). 
  5. Strachan, D. P. Hay fever, hygiene, and household size. BMJ 299, 1259-1260 (1989).
  6. Abdel-Gadir, A., Stephen-Victor, E., Gerber, G.K. et al. Microbiota therapy acts via a regulatory T cell MyD88/RORγt pathway to suppress food allergy. Nat Med 25, 1164–1174 (2019).
  7. Strachan, D. P. Hay fever, hygiene, and household size. BMJ 299, 1259-1260 (1989).
  8. World Health Organization. (2020, October 13). “Antimicrobial resistance.” Retrieved from
  9. Lathrop, S., Bloom, S., Rao, S. et al. Peripheral education of the immune system by colonic commensal microbiota. Nature 478, 250–254 (2011).

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