The Hygiene Hypothesis: Does Being Too Clean Increase Your Risk Of Developing An Autoimmune Disorder?

Is there such a thing as too clean? While it may seem like the upper limit of cleanliness could never exist, our intense desire to live in a perfectly clean world may not be as healthy as we once thought.

Over the past few decades, modern society has become obsessed with general hygiene, cleanliness, and anti-microbial protection. From hand sanitisers to the regular use of antimicrobial cleaning sprays on every possible surface, these intense cleaning behaviours have become incredibly normalized in our modern Westernized society. And while the idea of limiting our exposure to all bacteria seems like a great idea, in theory, it turns out that there are a variety of beneficial bacteria that we are now missing out on due to our ultra-clean expectations.

To better understand the impact of our societal high level of general hygiene, researchers have been conducting research to learn more about how limited exposure to microorganisms may impact our overall health. Known colloquially as “The Hygiene Hypothesis,” this theory suggests that there may be a connection between microbiota exposure and the risk of developing chronic health conditions like autoimmune disorders.

Many children born in wealthier countries are commonly exposed to a smaller number of bacteria, viruses, and allergens due to our heightened hygiene practices. And while this helps reduce the number of pathogen-based infections in young children, more research is being done to better understand the long-term impacts of this behaviour on the development of autoimmune disorders.

As this area of medical research continues to grow, more evidence from human and animal studies is beginning to emerge. So, while our hygiene efforts have been helpful in reducing the prevalence of pathogenic bacteria lurking around our commonly used spaces, they may also be causing more long-term harm than we think.

Understanding our immune system

Our immune system is an amazingly sensitive and intuitive thing. Made up of a collection of different organs, cells, and proteins throughout the body including the lymphatic system, adenoids, spleen, bone marrow, and more. The immune system is responsible for targeting and removing possibly harmful pathogens from the body¹.

There are two primary parts of the immune system: the innate and adaptive immune systems:

  • The innate system is the immune function that we are born with. Passed on to us from our mothers, this system consists of antibodies to fight off infections and pathogens that we are exposed to in our first months of life¹.

  • The adaptive system is a more robust system designed to create new protective cells and antibodies anytime the body is exposed to a new pathogen. With the help of a healthy innate immune system, the adaptive system can create successful immunity to life-threatening bacteria and viruses over time¹.

In order for a person to be healthy, they need to have adequate function of both immune systems throughout their lifetime. But, for our immune systems to grow and develop, we need to be regularly exposed to microorganisms for them to identify, respond to, and create lifelong antibody resistance. Without this exposure, malfunctions like the development of autoimmune disorders have become significantly more common, leading to the hypothesis that the pathogens around us may be contributing to our health and immunity more than we even know.

Autoimmune disorders are on the rise

Autoimmune disorders, which are characterized as diseases caused by immune system malfunctions that result in the immune cells targeting and damaging healthy body cells, are becoming more common around the world. While records are indicating that autoimmune disorders have been around for as long as human history, recent studies indicate that many different autoimmune disorders have increased in prevalence by up to 9% in the past few years². This sharp increase is only projected to increase over the coming years, which will result in the development of profound disability and increased medical care costs around the world.

Like many other chronic health conditions, where we live plays a role in our personal risk factors for developing an autoimmune disorder. In developed countries like The United States and the EU 5 where personal and general hygiene practices are baked into our societal behaviour, autoimmune disorders are on average a few percentage points higher than developing countries like Brazil and China³.

This global trend is also seen with specific autoimmune diseases like Crohn’s disease, lactose intolerances, and ulcerative colitis. For these digestive-based immune disorders, people living in developed countries like Australia, Canada, The United States, and The United Kingdom make up a large portion of the diagnosed cases today⁴.

The Hygiene Hypothesis — Is there such a thing as too clean?

In modern Western society, the common adage of just “rubbing some dirt” on our cuts and scrapes is no longer the general norm. Throughout human history, our immune system has been challenged time and time again by bacteria, viruses, parasites, fungi, and more that were commonly found in our public areas. With a limited understanding of microbiology and poor public health practices in the overcrowded early cities, it was very common for people to become ill as a result of experience with harmful bacteria. And while modern advancements in hygiene and cleanliness have resulted in a significant decline in pathogenic infections like cholera and typhoid, the trade-off may be an increased number of people living with autoimmune disorders.

Like we mentioned earlier, the health of our immune system is dependent on both the innate and adaptive systems. Exposure to bacteria is the single most important factor to the growth and development of these systems — and with increased anti-microbial practices being used today, many people born into our ultra-clean world are suffering health consequences. The hygiene hypothesis suggests that our current hygiene habits are exposing people to fewer total microorganisms — which includes the helpful and beneficial microorganisms we rely on for developing our microbiome. It is proposed that this lack of exposure to helpful microbiota is what causes a loss of immune balance throughout our bodies, leading to an increased risk of developing autoimmune disorders⁵.

Exposure to old friends (AKA bacteria) may be what is keeping us healthy

Current research estimates that the human being is made of 37 trillion human cells and 39 trillion bacteria⁶. Integral to our health, the “old friends” hypothesis suggests that these bacteria, viruses, and even parasites are essential in the creation of the unique microbiomes of each of the systems within our body. Without regular exposure to these helpful microorganisms, our immune system is unable to properly function, leading to an increased risk of developing chronic health disorders.

We collect our old friends throughout our entire lifetime, commonly from our surrounding environment. Starting at birth, we are exposed to these helpful bacteria from a variety of sources, including⁷:

  • Our mother's diet, how we were born, and maternal infections

  • Breastfeeding and formula feeding

  • Exposure to farm and house animals and pets

  • Siblings and daycare providers

  • Dust and pests in our home

  • Antibiotic use

Immunoregulation, which is our body’s innate ability to control the function of our immune system cells, is deeply dependent on the bacteria present in our microbiome. Without the presence of these helpful bacteria, the body is at an increased risk of developing cytokine stress responses to common social and pathological stressors. When this occurs, chronic inflammation within the body develops, triggering an immune system response, and leading to the possible development of an autoimmune disorder⁸.

So, as it turns out, some bacteria may be friends, not foe. And unfortunately, our current methods of cleaning do not differentiate between the two — meaning that we are wiping out just as many helpful bacteria as pathogenic ones. For individuals born into ultra-clean environments, the lack of exposure to these old friend bacteria is starting to be proposed as a potential cause for the increased prevalence of autoimmune disorders.

Evidence supporting the Hygiene Hypothesis

Research conducted on the hygiene hypothesis in both human and animal subjects has been a popular subject to explore in the past few decades. As medical researchers strive to better understand what causes many of our most common autoimmune disorders, these research studies are helping to better shape our understanding of the diseases.

In a study conducted in 2014, researchers explored the connection between allergen exposure in childhood and the incidence of wheezing diseases, which is a common precursor to developing asthma later in life. In this study, it was found that infants and children exposed to no common environmental allergens (things like dust mites, house pet dander, and even cockroaches) were more likely to experience recurrent wheezing over time⁹. Alternatively, infants who lived in homes with a higher number of common allergens were less likely to develop chronic wheezing⁹.

In another study conducted in 2007, research into the impact of anti-bacterial cleaning sprays on the risk of developing asthma was conducted. Collecting information about the current asthma status and the number of antibacterial cleaning sprays used in the home at least once a week, the study showed that long-term exposure to these cleaning products increased the risk of a person being diagnosed with asthma¹⁰. It is suggested that people living in homes with fewer microorganisms present due to regular disinfection from cleaning sprays were exposed to fewer beneficial bacteria, which in turn increased their risk of immunoregulation problems and autoimmune disorders.

There is still some disagreement in the medical community

Despite this compelling research, there is still pushback from many members of the medical community. A major reason that is commonly cited as proof against the theory is that it does not explain the development of all cases of autoimmune disorders. While it may play a role, there is also compelling evidence that there is a genetic component present that determines a person's individual risk factor for developing autoimmune disorders like asthma and food allergies.

Additionally, many people point to increased pollution and poor air quality for the sudden increase in asthma cases that began over 40 years ago. As an integral part of our environment, air quality and exposure to harmful chemicals can also very easily cause immune system disruption that can result in malfunction and disease¹¹.

Another common counterpoint, the hygiene hypothesis also cannot explain why children of immigrants are less likely to develop allergies, despite living in the same environment as their peers¹². This specific distinction may lend itself to the possibility that autoimmune allergies are most closely linked to our genetics rather than the environment, but more research needs to be conducted in order to better understand these complex topics.

So, taking an overall account of our current evidence and understanding, the current status of the hygiene hypothesis is only a proposed theory — but with further research into the topic, it may be able to be proven and integrated into our current understanding of chronic health disorders.

So what does this mean moving forward?

With all of this being said, it is clear that understanding autoimmune disorders is a complex and multi-faceted problem. While our modern ultra-clean lifestyle may be playing a role in increasing our risks of developing autoimmune disorders, it is not advised that you stop cleaning your house or start drinking unclean water to increase your exposure to more bacteria. This will just make you sick — and that is exactly what we are trying so hard to prevent with our current research!

Much like many other things in our world, there is an inherent balance between the benefits and drawbacks of living in a super clean environment. While this may be impacting the number of beneficial bacteria that we are exposed to on a daily basis, regular cleaning has also dramatically reduced the incidence of life-threatening bacterial and viral infections that previously plagued humanity for hundreds of years.

It is clear that this is not a black and white issue — with more research needing to be conducted in order to better understand the true impacts of reducing microorganism exposure and our general health. Hopefully, soon we will better be able to understand the true causes of autoimmune disorders, but until then, preventing opportunistic infections from common pathogens is worth the possible risks.

  1. Immune system | John Hopkins Medicine

  2. Report reveals the rising rates of autoimmune conditions | The British Society of Immunology

  3. Prevalence of diagnosed autoimmune conditions in selected countries as of 2019 | Statista

  4. Maps of the world showing distributions of incidence of quintiles of inflammatory bowel disease | Research Gate

  5. Inflammatory bowel diseases, the hygiene hypothesis and the other side of the microbiota: Parasites and fungi (2020)

  6. Scientists bust myth that our bodies have more bacteria than human cells (2016)

  7. The immunology of the allergy epidemic and the hygiene hypothesis (2017)

  8. Microbial ‘Old Friends’, immunoregulation and stress resilience (2013)

  9. Effects of early-life exposure to allergens and bacteria on recurrent wheeze and atopy in urban children (2014)

  10. The Use of Household Cleaning Sprays and Adult Asthma (2007)

  11. Air pollution alters immune function, worsens asthma symptoms | Berkeley News

  12. 99th Dahlem Conference on Infection, Inflammation and Chronic Inflammatory Disorders: Controversial aspects of the ‘hygiene hypothesis’ (2010)

The author, Claire Bonneau, is a medical writer and certified trauma operating room nurse.

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