Photo: Getting dirty may be healthy

We need to support conservation of natural areas and the diverse forms of life they contain, plant a variety of species in our yards, avoid antibacterial cleaning products and go outside in nature and get dirty – especially kids. (Credit: Jode Roberts)

By David Suzuki with contributions from Science and Policy Director Mara Kerry

For much of human history we lived close to the natural world. As civilization evolved we became increasingly urbanized, and most of us now live in cities. As we've moved away from nature, we've seen a decline in other forms of life. Biodiversity is disappearing. The current rate of loss is perhaps as high as 10,000 times the natural rate. The International Union for Conservation of Nature's 2008 Red List of Threatened Species shows 16,928 plant and animal species are threatened with extinction. This includes a quarter of all mammal species, a third of amphibian species and an eighth of bird species. And that's only among those we know about; scientists say we may have identified just 10 to 15 per cent of existing species.

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It can be a challenge to communicate why this loss is important. We know species diversity is critical to the healthy functioning of ecosystems that provide services on which humans depend. But could we live with fewer? Some would argue we could do without mosquitoes and other annoying critters. We could keep the ones we want and those that are useful to us. Do we need biodiversity to keep humans healthy?

According to an article in Conservation magazine, there is a link between biodiversity and human health. Ilkka Hanski and his colleagues at the University of Helsinki compared allergies of adolescents living in houses surrounded by biodiverse natural areas to those living in landscapes of lawns and concrete. They found people surrounded by a greater diversity of life were themselves covered with a wider range of different kinds of microbes than those in less diverse surroundings. They were also less likely to exhibit allergies.

What's going on? Discussion of the relationship between biodiversity and human health is not new. Many have theorized that our disconnection from nature is leading to a myriad of ailments. Richard Louv, author of Last Child in the Woods, says people who spend too little time outdoors experience a range of behavioural problems, which he calls "nature deficit disorder". It fits with theories of modern ecology, which show systems lacking in biodiversity are less resilient, whether they're forests or microbial communities in our stomachs or on our skin. Less resilient systems are more subject to invasion by pathogens or invasive species.

Hanski studied a region in Finland where few people move far. He randomly selected 118 adolescents in an equal number of homes. Some were in the city and others in woods or on farms. The team collected skin swabs from subjects and then measured the biodiversity of plants around each house. Their data revealed a clear pattern: higher native-plant diversity appeared to be associated with altered microbial composition on the participants' skin, which led in turn to lower risk of allergies.

Hanski and his colleagues found that one group of microbes, gammaproteobacteria, appears to be associated both with plant diversity and allergies. And it didn't matter whether they considered allergies to cats, dogs, horses, birch pollen or timothy grass. People with more diverse kinds of gammaproteobacteria on their bodies were less likely to have allergies.

The immune system's primary role is to distinguish deadly species from beneficial and beneficial from simply innocent. To work effectively, our immune system needs to be "primed" by exposure to a diverse range of organisms at an early age. In this way it learns to distinguish between good, bad and harmless. If not exposed to a wide array of species, it may mistakenly see a harmless pollen grain as something dangerous and trigger an allergic reaction. We also know that bacteria and fungi compete. Fungi are often associated with allergies, and it could be that high diversity of bacteria keeps the fungi in check.

A conclusive explanation for Hanski's observations is not yet available. More research is needed. But we know we evolved in a world full of diverse species and now inhabit one where human activity is altering and destroying an increasing number of plants, animals and habitats. We need to support conservation of natural areas and the diverse forms of life they contain, plant a variety of species in our yards, avoid antibacterial cleaning products and go outside in nature and get dirty — especially kids. Our lives and immune systems will be richer for it.

November 7, 2013

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Feb 26, 2015
2:15 AM

Loved reading this blog post.It’s very informative. Antibiotics

Jan 17, 2014
5:21 PM

Love this post!!! I have worked with Special Education Behaviour students for most of my teaching career and have seen first hand how nature and outside adventure benefits kids. Technology is being pushed in a big way in education today…it definitely has its place in assisting students with Spec. Ed. needs but I would pick a walk in the woods over an interactive whiteboard every time! The most difficult and challenging students always rise to the challenge. One of my best memories was seeing all of my high school “bad boys” in hip waders doing a stream survey with such curiosity in their eyes! Turn off the computers, tablets, and whiteboards…..and get dirty!

Nov 10, 2013
6:37 AM

in addition, a bacteria in the soil that we breath in while playing/gardening makes us SMARTER and HAPPIER! search ” Mycobacterium vaccae” and/or see

Nov 08, 2013
11:11 AM

Thank you David for such a great post. I can easily see the connection between loss in biodiversity and loss of lines of defence in our immune system. On a practical level however, I was wondering how much “dirty” a child could be allowed to become? I explored this thought a bit more.

For example, I believe a child can get very dirty in a farm. In the farms kids they are exposed on a daily basis with more potential antigens. Growing up in this environment is a tremendous challenge for the developing immune system. Do these kids tolerate challenges on their immune children better than those who lived in non-farm environments? Rob Dunn, the author of the article you cite, is familiar with the classic studies dealing with the early exposure of children to animals and farming and he mentions this in his review. I just wanted to draw the attention of the readers to these studies to emphasize the importance of early exposure of kids to natural world. 

J. Riedler and coworkers conducted  a study and published their results in Lancet (2001), trying to find out what is the relationship of “getting dirty” in the farm and the developing immune system. Getting “dirty” in their study was examined by the exposure of the kids to time spent in stables and the consumption of drinking farm milk. For example, the authors assumed ed that farm kids are “exposed to higher inhaled concentrations of endotoxin in stables and in dust from kitchens and mattresses than non-farming children” (p. 1132). In addition, they consume farm-milk which is processed for consumption in much different way than the way intended for consumption in the cities. 

More specifically the researchers tried to find out if the “Microbial burden in the first year of life could be crucial for the development of non-atopic immune responses” (p. 1129) and they found that farming has a strong protective effect against development of asthma, hay fever, and atopic sensitization.

Do you like to know more interesting results from their study? How about if we say that the “early exposure” does not begin from the time of birth but even earlier?  The same study found that mothers who were pregnant and visited stables frequently for regular farming choirs gave birth to children who were who developed less hay fever and became less sensitive than children whose mothers were not.

As you state in your post, “priming” of the immune system during the early parts of our life could be beneficial for us, that is exposure to a variety of antigens could be seen as beneficial too. Although the link between biodiversity loss and human health is not established conclusively, we need to be much more critical on the philosophy of the use of antibacterial products suggested by the industry in their quest for “oversimplifying” our life. In any case, I think that oversimplification is dangerous from any aspect you see it.

Riedler J. (2001). Exposure to farming in early life and development of asthma and allergy: a cross-sectional survey. Retrieved from

Nov 08, 2013
4:59 AM

Getting dirty may be healthy — Getting dirty used to be healthy today one would have to be worried about all the toxins we’ve released. I remember the bird life following the tractor — eating the worms oh and frogs lots of frogs.

All that was back when the nutrient cycle was still okay, today not many birds or frogs. As we don’t have a normal nutrient cycle, as the green revolution hailed as one of humanities greatest triumphs took care of that.

Which we are still pushing forward with just look at India we don’t learn.

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