Once upon a time, getting filthy was a childhood rite of passage. We made mud pies, dug holes to try to get to China, and emerged from the garden with twigs in our hair and microbes up our noses. These days, thanks to sanitiser, indoor lifestyles and a cultural obsession with cleanliness, many kids are better acquainted with iPads than insects. The result is a generation with squeaky-clean hands and suboptimal immune systems.
Excessive cleanliness is the essence of the hygiene hypothesis, first proposed by researcher David Strachan in 1989. He observed that kids in larger families – especially those with older siblings – had lower rates of allergies and immune disorders. He argued this was because they were more likely to swap bacteria through shared toys, sneezes and sibling squabbles. In other words, a bit of filth builds fortitude.
Fast-forward to today, and this theory has evolved into the biodiversity hypothesis – the idea that contact with a rich variety of environmental microbes (especially those found in soil and nature) helps calibrate our immune system, reduce inflammation and even protect against anxiety and depression.
And let’s be clear: soil is teeming with microbial life. A single teaspoon of healthy soil contains over 8 billion microorganisms – around the same number of humans on the planet – including bacteria, fungi, viruses and tiny invertebrates.
If you’re not into injecting soil bacteria (can’t imagine why not), the good news is gardening works too.
Finnish researchers transformed urban day care playgrounds by replacing the asphalt and gravel with soil and vegetation from coniferous forests. Within four weeks, the kids showed a measurable improvement in gut and skin microbiome diversity and an uptick in anti-inflammatory immune markers.  Other studies have found that families who garden regularly – and especially those with more diverse plant species in their gardens – have healthier gut bacteria and more robust immune profiles.
The soundtrack of nature: Not just pretty noise
It’s not just the microbes in nature that can heal us – the auditory experience is important as well.  Research from 2017, led by Cassandra Gould van Praag, found that listening to naturalistic soundscapes (such as birdsong or ocean waves) alters default mode network connectivity in the brain, reducing mind-wandering and enhancing present-moment focus.  Very good evolutionary reasons are behind this if you think about it. Birds chirping is a signal of safety. If they’re singing, no predators are around – so our threat systems relax. This may also explain why people feel so calm with water nearby. It’s not just poetic, but also neurological.
Biophilic design: Bringing nature in
As well as spending time outside in nature, bringing nature indoors also provides benefits. Biophilic design – the architectural and interior design approach that incorporates plants, sunlight, natural textures and views – has been shown to:
- increase focus and creativity
- reduce absenteeism
- improve mood and energy.
Office workers exposed to natural light and greenery report fewer sick days and greater job satisfaction. When I interviewed integrative medicine doctor Jenny Brockis on my podcast, she told me about a general practitioner in Perth who transformed his medical clinic with these principles – using natural light, plants and calming design to transform clinical care into a sensory healing experience – and saw dramatic improvements in patient mood and engagement.
Green scripts: Prescribing nature
Thankfully, we are now seeing the medical system belatedly catch on to this convincing research.  In the United Kingdom, green social prescribing is being integrated into the National Health Service (NHS). Patients with mental health issues or chronic illness are being prescribed time in nature – a ‘green script’ – instead of, or in addition to, medication. This is what they used to do in the 1930s in Britain – back to the future, eh? In Canada, PaRx is an evidence-based, nature prescription program that gives physicians the tools to prescribe outdoor time, based on hundreds of studies conducted on the health benefits of spending time in nature. Through PaRx, people are educated that time in nature busts stress, reduces the risk of chronic disease, controls blood pressure and increases health perception to a similar amount as a $10,000 raise! The program has been shown to improve the immune system of kids and literally make their brains bigger, increasing the size of the areas involved in memory and attention.
In the United States, ParkRx partners with the National Park Service, and has provided more than 500,000 park visits a year to more than 100,000 patients. A systematic review by Phi-Yen Nguyen and colleagues in 2023 found these interventions had led to improvements in mood, physical activity, sleep and cardiometabolic markers – and cost the health system very little.
This is what’s known as primary and secondary prevention – treating people with lifestyle interventions to prevent or manage health conditions – and it’s more effective, cheaper and a shitload less painful than waiting until people are really sick and treating them with surgical intervention or drugs (tertiary treatment), which is where the vast majority of the government healthcare spending goes.
Grounded: Why your nervous system needs a date with the dirt
We live on a giant, electrically charged rock that most of us spend too little time touching. Instead, we wear rubber-soled shoes, live in high-rise buildings or commute in sealed vehicles like climate-controlled sardine cans. Our skin rarely meets the surface of the Earth.
And, it turns out, that’s a problem. Because according to an intriguing body of research, being physically connected to the Earth’s surface – aka ‘grounding’ or ‘earthing’ – can lead to measurable improvements in inflammation, blood flow, sleep, stress, pain and even immune function.
Edited extract from The Hardiness Effect: Grow from stress, optimise health, live longer by Dr Paul Taylor (Wiley, $34.95), available at Amazon and leading retailers. Dr Taylor is a keynote speaker, podcast host and thought leader with post-graduate qualifications in psychology, exercise science, nutrition and neuroscience. Driven by the belief that we can grow from stress and live longer, healthier lives with the right habits, Dr Taylor helps individuals and teams unlock the power of psychophysiological hardiness to perform at their best. Visit https://www.paultaylor.biz/
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