The Old Friends Hypothesis: Are We Too Clean For Our Own Good?

issues-with-soapHumans have co-evolved with the complex microbial communities found in soil, water and the rest of the environment for millions of years, and it’s only recently that urban living and modern hygiene have disconnected us from the ecosystems found in nature. The Hygiene Hypothesis suggests that the increased use of hand sanitizers, soaps and cleaning detergents is largely to blame for the rapid rise in prevalence of allergies and other autoimmune disorders. The hypothesis basically says that our immune system expects a certain exposure to both good and bad germs during childhood and that hygienic measures have disrupted this education of the immune system. While it’s clear that lack of exposure to microbes from the environment has a significant impact on human health, the mechanisms underlying the hygiene hypothesis are now considered somewhat outdated, and researchers have rather begun talking about the adverse effects of losing microbial old friends.

The Old Friends Hypothesis says that the lack of bacterial exposure decreases the resilience and diversity of our own microbiome. While our hunter-gatherer ancestors were frequently exposed to a wide spectrum of microorganisms found in soil, water, mud and dirt, modern lifestyle has dramatically decreased our contact with bacteria, yeasts, parasites, and other microbes. Food manufacturers pasteurize and clean products to get rid of potentially harmful germs, and produce is often thoroughly washed or cooked before eaten. We’re also learned from an early age that hygienic measures are essential to avoid infectious disease, and harsh cleaning detergents are recommended for maintaining a healthy and bug free home.

However, several studies now suggest that although modern hygiene has helped combat several infectious diseases, decreased exposure to microbes also comes with some hidden costs. By removing ourselves from nature, our own microbial ecosystems suffer. The human body is inhabited by trillions of microorganisms that together make up the human microbiome. The health of this bacterial aura is partly determined by the microbial communities we interact with, and the typical human microbiome in the 21st century is probably very different compared to the microbiome of our paleolithic ancestors or that of non-industralized people (1).

Although excessive use of antibiotics is largely to blame for the decrease in diversity, modern hygiene and the disconnect from mother nature also play a significant role. We’re not only losing microorganisms that used to be a part of the human microbiome, but we have also reduced our exposure to transient microbes which drive immunoregulation and affect the genetic reportoire of the critters in our body through horizontal gene transfer.

Microbial genes are essential to our health

While the specific types of bacteria that inhabit the body are important, the entire genome of the our microbial rainforest is probably even more crucial to our health. The genetic repertoire of the human host is miniscule compared to that of our resident microbes, and this second genome contributes essential functions that stretch far beyond the capabilities of the human host.

Humans evolved eating dirty food with trillions of clinging soil microbes.

Humans evolved eating dirty food with trillions of clinging soil microbes.

One of these important functions is the production of enzymes needed to break down otherwise indigestible food components. With the exception of starch, all complex carbohydrates found in plants (polysaccharides) are broken down by hundreds of different species of bacteria in the gut. Plant roots and leaves are naturally rich in soil microbes, and when our hunter-gatherer ancestors ate plants directly from nature they didn’t just ingest vitamins, minerals and dietary fibers, but also hundreds of species of bacteria. Some of these microbes took up root in their gastrointestinal tract or transferred genes to the critters living in gut biofilms. These genes became a part of the microbiome and helped us produce the necessary enzymes to digest the complex polysaccharides found in plants.

While soil and dirt also contain potentially pathogenic bacteria, a healthy microbiome serves as a natural protection against harmful germs. This is also the reason why some people are especially vulnerable to infection from pathogens, while others rarely get sick. Hygienic measures are often recommended to avoid infections, but the fact is that a healthy microbiome is usually the best protection against communicable disease, not soaps and hand sanitizers.

Reduced exposure to bacteria increases the risk of autoimmune disease

There is now plenty of research to suggest that the loss of microbial old friends leads to poor immunoregulation  (2,3). Studies show that people growing up on farms have less risk of autoimmune disease than people living in urban settings, and that this increased protection stems from environmental exposure to microbes (4). It’s also been shown that children who grow up with pets have reduced risk of developing allergies compared to other kids, because they pick up germs from the animals (5).

While most of the research on the old friends hypothesis has focused on autoimmune disorders, we know that the human microbiome affects all aspects of our health and well-being, and it’s therefore safe to say that making some new microbial friends is a good idea if you want to decrease your risk of getting both non-communicable and communicable diseases.

This doesn’t mean that you have to stop washing your hands after you go to the bathroom or eliminate all personal care products. However, being less hygienic, throwing hand sanitizers in the trash and replacing traditional body care products with natural alternatives is a good start for most people. Eating some dirty vegetables from the garden, farmers market or other trusted source can also help you reconnect with some old companions (6).

Personal care products potentially disturb the microbiome and increase exposure to harmful chemicals

Besides reducing our contact with bacteria and worms, hygienic products can also alter the bacterial communities on our body. Our skin and hair are complex microbial ecosystems, and just like when we disrupt the gut microbiota with broad-spectrum antibiotics and highly processed food, hand sanitizers and frequent use of other hygienic products probably change the balance of bacteria living on the skin (7). The problem at the moment is that although there are thousands of articles discussing dysbiosis in the gut, mouth, lungs and vagina, few studies have looked at the relationship between body care products and changes in the bacterial communities on the skin.

However, we do know that the skin microbiome is colonized by a diverse collection of microorganisms that help educate billions of T cells and protect us from harmful germs (8). The detrimental effects of skin dysbiosis is especially seen in disorders such as acne, atopic dermatitis and psoriasis, where the microbial communities are altered (9,10). While all of these disorders are linked with low-grade chronic inflammation, the end result is changes to the bacterial communities on our body.

So, although we need more studies on the skin microbiome, it’s safe to assume that disrupting the microbial ecosystems with harsh soaps and anibacterial gels on a frequent basis is not a good idea.

Body care products often contain chemical ingredients that lack safety data.

Body care products often contain chemical ingredients that lack safety data.

Besides the effects on the microbiome, several reports also show that common personal care products contain chemical ingredients that lack safety data (11). While reproductive or developmental toxicants in cosmetics aren’t my area of expertise, I’m always sceptical to traditional body care products that contain phthalates, parabens, triclosan and other potentially toxic ingredients.

While most people aren’t prepared to eliminate personal care products completely, ditching hand sanitizers and replacing traditional moisturizers, deodorants and liquid soaps with natural alternatives will remove most of the chemical load and reduce the adverse effects on the microbiome. I’ve found that products such as Dr. Bronner’s liquid soap (body, hair and hands), Dr. Bronner’s shaving gel, deodorants made from crystallized natural mineral salts, and coconut butter (moisturizer) are excellent organic alternatives to traditional body care products.

The takeaway is to remember that our body is a superorganism and that a lack of exposure to microorganisms from the environment  can jeopardise the health of our own ecosystem!


  1. […] intolerance also published last week, Dr. Stefano Guandalini talks about the connection between the hygiene hypothesis, dysbiosis, and the rise of celiac disease. Even though his take on the hygiene hypothesis seems […]

  2. […] Humans are very similar in terms of our human genome, but the microbiome can vary significantly from one person to another. While both of these genomes were developed in the ancestral natural environment, the microbiome is more susceptible to changes in environment and lifestyle than the human genome. The typical human microbiome of the 21st century is probably very different from that of our hunter-gatherer ancestors, and it’s likely that some old friends are now gone forever. […]

  3. […] important to remember that several lifestyle factors, such as sun exposure, physical activity, and exposure to microorganisms, can help explain the excellent health of non-westernized populations eating high-fat diets, and we […]

  4. […] Does this mean that we have adapted to grains, milk, and other foods banned from the paleo diet? Not so fast… By now it’s well accepted that the western lifestyle is a master manipulator of the microbiome, and there are now thousands of studies showing that modern hygiene, processed foods, antibiotics, c-sections, etc. perturb the microbial ecosystems that live in and on our bodies (17,18,19). The westernized microbiome lacks diversity and resilience and is most likely only a faint imprint of the microbiome of our prehistoric ancestors. Loss of microbial diversity and dysbiosis (imbalance) have now been linked to a multitude of diseases and are without a doubt a driving force behind the increased rates of autoimmune disorders, food sensitivities, and food allergies now seen in the industrialized world (18,20,21). Especially relevant to this article is the increased prevalence of grain- and gluten-related disorders, which have been linked to gut dysbiosis and a loss of microbial old friends. […]

  5. […] rest of the environment, and that exposure to bacteria is essential to our health and well-being (11,12). I try to avoid being to hygienic, and use natural body care products. I also eat fermented […]

  6. […] and increased risk of autoimmune disease later in life, has now gotten its successor in the old friends hypothesis. This hypothesis, which is supported by more and more compeling evidence, states that a lack of […]

  7. […] Food hygiene Some studies suggest that we’ve become too clean, and that we could benefit from dirtying up our diets and reconnecting with some old friends. […]

  8. […] clean homes and adopting modern hygienic practises. This disconnect has resulted in a loss of  microbial old friends that used to be a part of the ancestral human […]

  9. […] We’ve probably lost some key species that used to be a part of the ancestral microbiome. […]

  10. […] typical westerner (4)), they spend plenty of time outdoors, they live in close contact with nature (“adequate” exposure to microbes), and they eat a diet that’s exclusively composed of nutritious whole […]

  11. […] typical westerner (4)), they spend plenty of time outdoors, they live in close contact with nature (“adequate” exposure to microbes), and they eat a diet that’s exclusively composed of nutritious whole […]

  12. 8 Dirty Secrets about Restaurants You Can’t Know | thewowfact says:

    […] Image Source: […]

Do you have any comments or questions pertaining to the article? If so, please feel free to post them below. Note: Comment moderation is in effect. Spam, rants, hateful remarks, etc. will be deleted.


Get every new post delivered to your Inbox

Join other followers: