Getting Hands Dirty: Touching soil, grass, trees and other natural materials may do more than connect us with the outdoors. Emerging research suggests that regular contact with nature can increase the diversity of microbes living on our skin and may influence how the immune system functions.

For many people, getting dirty is something to avoid.

We wash our hands.

Clean our homes.

Avoid muddy surfaces.

And tell children to keep dirt away from their clothes.

But scientists studying the relationship between nature and human health are increasingly interested in a different idea: perhaps we should not be trying to eliminate every encounter with the microbial world around us.

Research from Finland and elsewhere suggests that contact with soil, plants and other natural materials can alter the communities of microorganisms living on our skin.

And those changes may have consequences beyond the skin itself.

What Happens When You Touch Soil?

One experiment led by ecologist and nature-health researcher Mira Grönroos asked participants to rub their hands with soil, peat and moss for just 20 seconds.

Researchers then examined the microorganisms living on their skin.

The result was striking.

The number and variety of microbes on participants’ hands increased, and the changes remained detectable even after they rinsed their hands with ordinary tap water.

That may sound undesirable.

After all, most people associate bacteria with illness.

But the human body naturally hosts enormous communities of microorganisms, and not all bacteria are harmful.

In fact, microbial diversity may be an important part of maintaining a healthy skin ecosystem.

Not All Bacteria Are Bad

Our skin is home to a complex community of microorganisms.

These microbes interact with one another and with the human body.

A diverse microbial community can help prevent potentially harmful organisms from becoming dominant.

That means the goal should not necessarily be to eliminate every microorganism.

Instead, researchers are investigating whether maintaining a healthy and diverse microbial environment can help support the body’s natural defences.

This idea is particularly important because modern lifestyles can reduce people’s everyday exposure to natural environments.

The Biodiversity Hypothesis

The research forms part of a broader scientific idea known as the biodiversity hypothesis.

The hypothesis proposes that regular exposure to diverse natural environments, including plants, soil and the microorganisms associated with them, can influence the human microbiome and immune system.

The theory also suggests that declining biodiversity could have consequences for human health.

As cities expand and people spend more time indoors, everyday contact with soil, vegetation and naturally occurring microbes may become less common.

Scientists are investigating whether this reduction in exposure could partly contribute to changes in immune-related conditions.

The evidence is still developing, but the question has become increasingly important.

Why Children May Benefit From Playing in Nature

Some of the most interesting research has involved children.

At Aurinkolinna daycare centre in central Finland, children spend substantial amounts of time playing outdoors.

Their environment includes trees, bushes, sand, woodchips and puddles.

And yes plenty of mud.

Scientists are studying whether this type of regular contact with natural environments affects children’s microbiomes and immune systems.

The work forms part of the Vahvistu research project, involving 43 Finnish daycare centres.

Researchers are examining changes in microorganisms found on children’s skin, saliva and faeces, alongside biological markers from blood and hair.

The goal is to understand what happens when natural environments become part of children’s everyday surroundings.

What Happened When Forest Floors Were Added to Daycare Yards?

Earlier research led by environmental scientist Marja Roslund took a similar approach.

Researchers introduced elements of a forest floor, including peat and planting boxes, into a daycare environment.

Children played in these settings regularly, and researchers compared their microbial profiles with those of children who played in more conventional paved environments.

After sustained exposure, the children who played in the forest-floor environment had greater microbial diversity on their skin.

The findings remained apparent a year later.

That is important because it suggests the effects of environmental exposure may extend beyond the immediate moment when a child touches soil.

More Microbial Diversity Could Help Keep Harmful Bacteria in Check

Researcher Roslund has suggested that a diverse microbial community can make it harder for potentially harmful bacteria to dominate the skin.

The basic idea is relatively straightforward.

When many different microorganisms occupy an environment, potentially harmful organisms have less opportunity to take over.

Scientists are still studying exactly how these microbial communities interact, but the findings have added to the growing interest in the relationship between biodiversity and health.

Could Soil Exposure Affect the Immune System?

The research becomes even more interesting when scientists look beyond the skin.

In one study, children played in a sandbox containing microbially diverse soil.

Another group used a similar-looking sandbox with less microbial diversity.

As expected, the children exposed to the richer soil developed greater diversity in certain bacteria on their skin.

But researchers also detected changes in cytokines in their blood.

Cytokines are signalling molecules involved in immune responses.

The observed changes were consistent with processes involved in immunoregulation, which refers to the body’s ability to control immune activity and respond appropriately to threats.

That does not mean playing in soil prevents disease.

It does, however, suggest that environmental microbial exposure may interact with the immune system in measurable ways.

Could This Reduce Allergies or Asthma?

This is one of the most interesting questions and also one where researchers urge caution.

The findings have raised the possibility that exposure to diverse natural environments could influence the development of immune-related conditions.

But scientists cannot yet say that allowing children to play in soil will prevent asthma, eczema or allergies.

The research provides clues about possible mechanisms.

It does not establish a simple cause-and-effect relationship.

That distinction is important.

The Immune System Needs Balance

The immune system has a difficult job.

It must respond effectively to harmful threats while avoiding excessive reactions to harmless substances.

An immune system that is too weak can leave the body vulnerable to infections.

An immune system that reacts excessively can contribute to inflammatory or immune-mediated conditions.

The research into environmental biodiversity is therefore interested not simply in making immunity “stronger”.

It is about whether exposure to diverse microorganisms may help the immune system develop and regulate itself appropriately.

Gardening Could Also Provide a Microbial Boost

You do not necessarily need to live beside a forest to experience some of these environmental exposures.

Gardening may provide another accessible opportunity.

In one study, adults grew vegetables indoors during winter.

Some participants used soil with greater microbial diversity, while others used similar-looking soil with fewer microorganisms.

The participants cared for their plants every day for a month.

Researchers found that those working with the more microbially diverse soil experienced an increase in bacterial diversity on their skin.

They also showed changes in anti-inflammatory cytokines in their blood.

The comparison group did not show the same changes.

That finding is particularly interesting because it suggests that contact with nature does not necessarily require a wilderness adventure.

A small garden may provide a meaningful form of everyday environmental exposure.

Green Spaces Could Change the Microbes on Your Skin

The potential benefits may even extend to workplaces.

Researchers have experimented with bringing living plants into indoor environments.

In one study, Finnish offices were fitted with green walls made from living plants.

After two weeks, workers showed increased microbial diversity on their skin.

Researchers also observed lower levels of some pro-inflammatory cytokines in their blood and an increase in Lactobacillus bacteria on the skin.

The findings suggest that incorporating living vegetation into built environments may influence the microbial environment people encounter every day.

But again, the results should be interpreted as evidence of biological changes not proof that office plants prevent disease.

Why Modern Cities May Need More Nature

One of the broader implications of this research concerns urban design.

Modern cities often separate people from natural environments.

Concrete replaces soil.

Paved playgrounds replace forest floors.

Buildings replace vegetation.

And children may spend more time indoors than previous generations.

Researchers are therefore asking whether cities could be designed to provide more opportunities for everyday contact with nature.

That could include:

• More trees and vegetation
• Natural playgrounds
• Community gardens
• Soil and planting areas
• Woodchip or natural-surface spaces
• Accessible parks
• Green areas around schools and workplaces

The goal would not be to force people to spend hours in the wilderness.

Instead, nature could become part of everyday life.

Nature Contact Does Not Have to Be Complicated

One of the most appealing aspects of this research is how simple the potential intervention can be.

You do not necessarily need expensive equipment.

You do not need a gym membership.

And you do not have to travel to a remote forest.

Simple activities such as gardening, sitting on grass, touching tree bark or allowing children to explore natural outdoor environments may provide opportunities for contact with the microbial world.

Researchers involved in the work describe nature contact as relatively low-risk while acknowledging that more research is needed to understand the precise health effects.

Should Parents Stop Worrying About Mud?

Parents should still pay attention to hygiene and safety.

The research does not suggest that children should be encouraged to deliberately expose themselves to contaminated environments.

There is an important difference between natural environmental exposure and contact with obviously unsafe material.

Children should still wash their hands before eating and after potentially hazardous activities.

But ordinary outdoor play does not necessarily need to become a battle against every speck of dirt.

A little mud may be part of a healthy childhood.

The “Five-Second” Mindset May Be Too Simple

The interesting scientific question is not whether dirt is inherently healthy.

It is whether regular interaction with diverse natural environments can influence the human microbiome and immune system.

The research suggests there may be something important happening.

But it does not mean that every patch of soil is beneficial or that more bacteria automatically means better health.

Context matters.

Frequency May Matter More Than One-Off Exposure

The research also suggests that microbial changes can be temporary.

The increase in skin microbial diversity following a brief soil exposure was not necessarily permanent.

That raises an important possibility.

Rather than one dramatic encounter with nature, repeated everyday exposure may be more meaningful.

That could help explain why activities such as gardening and regular outdoor play are particularly interesting to researchers.

What Scientists Still Don’t Know

Despite the promising findings, there are major unanswered questions.

Scientists still need to determine precisely how environmental microbial exposure affects the immune system over long periods.

They also need to establish whether the observed biological changes translate into meaningful reductions in disease.

For conditions such as asthma, eczema and allergies, researchers cannot yet conclude that contact with nature directly prevents them.

The current evidence is better understood as a growing body of research pointing towards a possible relationship.

More Research Is Needed

Longer studies are particularly important.

Researchers need to understand whether changes in the microbiome remain stable.

They also need to establish which types of microorganisms matter most and how much exposure is necessary.

The Vahvistu project and related research could provide valuable evidence as scientists continue investigating these questions.

A Different Way to Think About Cleanliness

Modern hygiene has transformed public health.

Clean water, sanitation, handwashing and infection control remain essential.

But the emerging research highlights a different concept: being clean does not necessarily mean eliminating all microbial exposure.

Humans evolved alongside complex microbial ecosystems.

The challenge may be finding an appropriate balance between protecting ourselves from dangerous pathogens and maintaining healthy interactions with the microbial world around us.

That is particularly relevant as more people live in highly urbanised environments.

Getting your hands dirty may not be as unhealthy as many people assume.

Research from Finland and elsewhere suggests that contact with soil, plants and other natural materials can increase microbial diversity on the skin and may influence markers involved in immune regulation.

Studies involving children have found differences in skin microbiota after exposure to forest-floor environments and microbially diverse soil.

Research involving gardening and green walls has produced similarly interesting findings in adults.

But the science does not yet prove that touching soil prevents asthma, allergies, eczema or other immune-related diseases.

The most reasonable conclusion is more modest.

Regular contact with diverse natural environments appears to be biologically interesting, potentially beneficial and relatively easy to incorporate into everyday life.

So the next time a child comes home covered in mud after playing outside, the mess may not be the only thing they brought home.

They may also have given their microbiome a little taste of the natural world.

Research suggests that touching soil, plants and natural environments may increase skin microbial diversity and influence immune function. Discover what scientists know so far.

Getting Hands Dirty

Source: BBC

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