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Effects of Green Environment Exposure on Stress-Related Human Skin Gas Emissions

This study demonstrates that a one-hour rest in a green space significantly reduces stress-related skin gas emissions (ammonia and allyl mercaptan) while increasing plant-derived monoterpenes in healthy individuals, suggesting that green environments modulate physiological stress responses and that skin gas analysis offers a non-invasive method for assessing such effects.

Original authors: Joe Kochi, Maho Muramatsu, Yoshika Sekine, Kenji Tsurumi

Published 2026-07-25

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Joe Kochi, Maho Muramatsu, Yoshika Sekine, Kenji Tsurumi

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine your body is like a bustling city. Just as a city releases exhaust fumes, steam from factories, and the smell of street food into the air, your skin constantly releases a invisible cloud of gases. Scientists call this "skin gas." Some of these gases are like the city's pollution: when you are stressed, tired, or anxious, your body releases specific "stress fumes" like ammonia (which smells sharp, like cleaning fluid) and allyl mercaptan (which smells like onions or garlic). On the other hand, when you are calm, your body's "exhaust" changes.

Now, imagine your city has a special park where the trees release their own pleasant, fresh scents—like pine needles or citrus peels. For years, we've known that visiting these parks makes people feel better and lowers their heart rate. But scientists have been wondering: does the park actually change the invisible "exhaust" your body is pumping out? Does sitting among the trees actually clean up your personal atmosphere? This is the question researchers set out to answer by treating human skin like a tiny, living weather station.

The Great Skin Gas Experiment

In this study, a team of researchers from Tokai University and the Kawasaki Environmental Research Institute decided to play detective with human sweat and skin gases. They wanted to see if taking a break in a green park could actually stop your body from releasing those "stress smells."

The Setup: Stress, Then Chill
The researchers gathered 13 healthy volunteers and put them through a "stress test." First, everyone had to go into a meeting room and give a short speech, followed by a group discussion. This was designed to make their hearts race and their stress levels spike.

After the stress, the volunteers were split into two groups for a one-hour "recovery" period, but here is the twist: it was a crossover experiment.

Group A went to the stress room in the morning, then relaxed in a beautiful, tree-lined park (Ikuta Ryokuchi Park) in the afternoon.
Group B did the opposite: they relaxed in the park in the morning and went to the stress room in the afternoon.
The control group (or the "boring" group) spent their recovery time sitting in a closed meeting room with no view of the outside world, while the "green" group walked or sat among the trees.

During these times, the researchers stuck special "passive samplers" (like high-tech sticky pads) onto the volunteers' forearms to catch the gases coming off their skin.

The Big Discovery: The Park is a Filter
When the researchers analyzed the data, they found a dramatic difference between the two environments.

The Stress Smells Disappeared: When the volunteers rested in the green park, the amount of ammonia (the sharp, cleaning-fluid smell) and allyl mercaptan (the onion-like smell) coming off their skin dropped significantly.
- Ammonia levels fell by about 67%, dropping from roughly 1.8 × 10² ng cm⁻² h⁻¹ during stress to just 60 ± 41 ng cm⁻² h⁻¹ after the park break.
- Allyl mercaptan levels plummeted by about 76%, going from 5.1 ± 4.5 ng cm⁻² h⁻¹ down to 1.2 ± 1.3 ng cm⁻² h⁻¹.
- In contrast, the people who stayed in the meeting room saw almost no change in these stress smells. Their "exhaust" remained high.
The Good Smells Arrived: While the bad smells vanished, something else happened in the park group. The skin started releasing more monoterpenes (compounds like α-pinene, β-pinene, and limonene). These are the fresh, piney, and citrusy scents that trees naturally give off.
- The researchers found that the more these tree scents were released from the skin, the less stress gas was coming out.
- It seems the volunteers inhaled the fresh air of the park, and their bodies absorbed those tree scents, which then traveled through their blood and were released back out through their skin.

What Does This Mean?
The study suggests that spending just one hour in a green space doesn't just make you feel relaxed; it physically changes how your body reacts to stress. The "stress fumes" (ammonia and allyl mercaptan) are linked to your body's "fight or flight" mode (sympathetic nervous system). When you are in a park, your body seems to switch to "rest and digest" mode (parasympathetic nervous system), which stops the production of those stress smells.

The researchers propose that breathing in the tree scents (monoterpenes) might be the key. These scents appear to help your body calm down, which in turn stops the skin from releasing the "onion" and "cleaning fluid" odors associated with anxiety.

The Bottom Line
This paper doesn't claim that a park is a magic cure-all, but it offers a fascinating new way to look at stress. It suggests that skin gas analysis could be a non-invasive "smoke detector" for stress levels. If your skin is pumping out less ammonia and more pine-scent, you might be in a state of true physiological calm. So, the next time you feel stressed, the science suggests that a walk among the trees might not just clear your mind—it might literally clear the air around you.

Technical Summary: Effects of Green Environment Exposure on Stress-Related Human Skin Gas Emissions

Problem Statement
Urban living exposes individuals to a confluence of environmental and psychosocial stressors, including noise, pollution, and high population density, which contribute to sustained physiological stress responses. While "nature-based solutions" such as urban greening are promoted to improve health and well-being, the specific physiological mechanisms by which green space exposure mitigates stress remain partially understood. Conventional markers like salivary cortisol and heart rate variability are well-documented, but the impact of green environments on human skin gas emissions—volatile compounds released from the skin that reflect metabolic and stress states—has not been thoroughly investigated. Specifically, the relationship between green space exposure and the dermal emission of stress-related malodorous compounds (ammonia and allyl mercaptan) versus plant-derived aromatics (monoterpenes) is unknown.

Methodology
The study employed a randomized crossover design to investigate changes in skin gas emissions following stress induction and subsequent recovery.

Participants: 13 healthy volunteers (6 in spring, 7 in autumn) underwent the protocol.
Setting: Experiments were conducted at Ikuta Ryokuchi Park, Kawasaki City, Japan, and an indoor meeting room within the same facility.
Protocol:
1. Stress Induction: All participants underwent a standardized 1-hour stress-induction period in the meeting room involving public speaking and group discussions/debates.
2. Recovery Phase: Participants were randomly assigned to one of two 1-hour recovery conditions:
  - Experimental: Resting in a designated green space within the park (tree-lined path, woodland vegetation, minimal traffic noise).
  - Control: Resting in the indoor meeting room with windows closed and blinds drawn to exclude visual contact with the outdoors.
3. Counterbalancing: The order of conditions was counterbalanced between participants and across seasons (spring and autumn) to minimize order effects.
Sampling & Analysis:
- Skin gases were collected from the forearm using passive flux samplers (PFS) for 1-hour intervals during both stress and rest periods.
- Target Compounds:
  - Stress-related: Ammonia (inorganic) and Allyl mercaptan (volatile sulfur compound).
  - Green space-related: Monoterpenes ( $\alpha$ -pinene, $\beta$ -pinene, and limonene).
- Quantification: Ammonia was analyzed via ion chromatography (IC); Volatile Organic Compounds (VOCs) were analyzed via gas chromatography–mass spectrometry (GC-MS).
- Controls: Dietary intake was standardized (carbohydrate-heavy) to minimize protein-induced ammonia variations; indoor temperature was controlled (18–19°C).

Key Results
The study found distinct differences in dermal emission fluxes between the green space and indoor control conditions:

Reduction in Stress-Related Compounds:
- Ammonia: In the green space group, dermal ammonia emission flux significantly decreased from $1.8 \times 10^2 \pm 2.0 \times 10^2$ ng cm⁻² h⁻¹ (stress) to $60 \pm 41$ ng cm⁻² h⁻¹ (rest), a reduction of approximately 67% ( $p = 0.035$ ). No significant change occurred in the control group.
- Allyl Mercaptan: The combined flux in the green space group decreased from $5.1 \pm 4.5$ ng cm⁻² h⁻¹ to $1.2 \pm 1.3$ ng cm⁻² h⁻¹, a reduction of approximately 76% ( $p = 0.0046$ ). The control group showed no significant change.
Increase in Green Aroma Compounds:
- Dermal emissions of $\alpha$ -pinene, $\beta$ -pinene, and limonene significantly increased during the rest period in the green space ( $p = 0.017$ , $0.031$, and $0.035$, respectively).
- The emission flux order was $\alpha$ -pinene > limonene > $\beta$ -pinene.
- No notable changes were observed in the control group.
Correlation: A marked inverse relationship was observed: as dermal monoterpene emissions increased, emissions of ammonia and allyl mercaptan decreased.

Key Contributions

Novel Physiological Marker: This is the first study to apply skin gas analysis as a physiological marker in a crossover study of green environment exposure. It establishes skin gas profiles as a non-invasive indicator of stress modulation.
Mechanistic Insight: The results suggest that green space exposure modulates skin gas profiles by shifting the autonomic nervous system toward parasympathetic dominance. The reduction in ammonia (linked to sympathetic dominance) and allyl mercaptan suggests a suppression of stress-induced metabolic pathways.
Exogenous-Uptake Hypothesis: The study provides evidence that inhaled monoterpenes from the green environment are absorbed, distributed via the bloodstream, and subsequently released through the skin, serving as a biomarker for environmental exposure and potential stress relief.

Significance and Claims
The authors claim that this study elucidates the physiological effects of green environments on human stress responses through a non-invasive, chemical lens. The findings support the integration of environmental exposure assessment with physiological monitoring.

Stress Reduction: The study demonstrates that a 1-hour exposure to a green space significantly reduces the dermal emission of stress-related malodorous compounds while increasing the emission of plant-derived aromatics.
Body Odor Implications: While olfactory evaluation was not conducted, the authors posit that the shift in skin gas composition (less ammonia/allyl mercaptan, more monoterpenes) likely contributes to an improvement in body odor associated with stress.
Limitations: The authors acknowledge limitations regarding the intensity and duration of exposure (1 hour) and the need for validation across diverse green spaces and shorter exposure times relevant to urban workers.

In conclusion, the paper asserts that skin gas analysis offers a sensitive, non-invasive tool to quantify the restorative effects of nature, providing novel insights into how green infrastructure can modulate human physiological stress responses.

The Great Skin Gas Experiment

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