Pollution in Climbing Gyms: The Counter-Investigation

In the middle of spring, a scientific study threw the private climbing gym industry into chaos. Widely picked up by mainstream media, the research left indoor climbers feeling their training grounds were as polluted as a roadside. It was high time Vertige Media carried out its own counter-investigation. Here’s what we uncovered between Paris, Switzerland, Isère, Toulouse, and the Dolomites.

"Wait, there’s a problem—they shouldn’t be running at this hour." When Pierre Serin flips the switch to activate his turbines, he turns around with a playful look. You might think he'd been caught with his hand in the cookie jar. But with astonishing calmness, he gestures to an open window: "Anyway, natural airflow still works best."

Serin, owner of Solo Escalade—a private bouldering gym in Toulouse—would have good reason to worry. On that May morning, only a few days had passed since a study had sent shockwaves through his industry. This serious research, published on April 24 in the prestigious scientific journal Environmental Science & Technology Air (ACS ES&T Air), drew a troubling conclusion: climbing shoe rubber releases concerning chemical additives into the air of climbing gyms. Yet, sitting in his gym located in an industrial zone, Pierre Serin appears relaxed. By his own admission, no clients have cancelled their memberships. Nobody panicked. "Customers reacted very well," he explains. "We decided to proactively communicate about the study before anyone asked, reassuring clients and parents we'd work even harder. They trusted us."

Media-driven pollution

Across one entire wall of Solo Escalade’s 2400-square-meter climbing space, windows are wide open. At the back, three kids twist their fingers on a Kilter board, while employees brush holds or serve coffee. Sweeping an arm across the gym, Serin explains: "We can get crowded, and sometimes you can actually see chalk or rubber particles floating around." To purify the air, Serin ventilates the space multiple times a day with powerful turbines capable of renewing almost all the gym's atmosphere several times per hour. But after peak times—mainly evenings and weekends—the turbines stop, and thorough cleaning begins. "We have two employees dedicated solely to cleaning," says the manager. "It's brutal physically. The person who cleans the mats—I don't know how they keep it up. Constantly vacuuming, scrubbing corners… It's hellish." The entrepreneur, who employs 17 people, says every month and a half his staff carries out what's called "the big cleanup": "We take everything apart, clean every piece, and then rebuild it all."

Pierre Serin, founder of Solo Escalade in Toulouse © Vertige Media

Pierre Serin wears the smirk of a seasoned business owner who's seen it all. At 62, he’s watched many health scares rock the indoor climbing world. Yet this one undeniably spread faster. Within days following the academic publication, a wave of influential French media picked up the story, most opting for sensational headlines: "Climbing gyms more polluted than roadsides." Reached by phone by Vertige Media, one of the study’s lead authors, Thibault Masset, expresses regret. "I didn't anticipate such a response," he admits. "Many media outlets exaggerated our results and created alarmist scenarios." This researcher from Lausanne’s École Polytechnique Fédérale (EPFL) even finds himself debunking misinformation and challenging simplified narratives among journalists. An example? "It's misleading to claim climbing gyms are more polluted than roadsides. Standing by a road, you inhale tire additives, combustion particles, and numerous other pollutants. You must compare like with like."

“We’re not toxicologists. We have no scientific means to prove what we measured is harmful to humans.” — Thibault Masset, study author

Similarly, when a journalist wrote that it was "scientifically proven" that the particles detected by Masset and his colleagues were "dangerous to humans," he immediately contradicted it. "We're not toxicologists. We have no scientific means to prove that what we've detected is harmful to human health. It's worrying because one study found negative impacts on aquatic species, but human effects remain entirely unproven." To determine this, researchers would need to collaborate with toxicology experts—to study whether these substances are absorbed, penetrate skin, enter lungs, or reach the bloodstream when inhaled.

The media storm undoubtedly shook the private climbing gym industry. As a climber himself, Masset had tried to offer solutions within the study itself, strongly recommending better ventilation, cleaning, and hold washing. He still encourages collaborations with climbing gyms to produce further research. Since RDCs (Rubber-Derived Chemicals) come primarily from shoe friction against walls, it didn’t take long for the industry to turn towards manufacturers.

Mystery and Rubber Balls

When Frédéric Tuscan learned about the ACS ES&T Air study, the founder and CEO of 9A Climbing, a European giant in climbing footwear (including iconic French brand EB), felt immediate pressure. Reached by Vertige Media, he’s open about his anxiety. "When I read the study, I found it alarming. I immediately knew our entire company would be deeply concerned in the days ahead." Clients—particularly worried gym owners—soon flooded him with calls.

Though aware the rubber used in climbing shoes is petrochemical-based and thus environmentally problematic, Tuscan "never imagined rubber dust could remain suspended, react with ozone, and accumulate significantly." Responding pragmatically, Tuscan seized the moment. Last year, speaking on Radio France, he’d already mentioned exploring bio-based materials. Has the study accelerated that? "Clearly," he confirms. "We’ve already scheduled meetings with producers of plant-based plastics."

“Basing R&D efforts on such incomplete research worries me. We don’t know what rubber they tested, and they only sampled nine gyms—including some Austrian ones known to be crowded and poorly ventilated.” — Frédéric Tuscan, CEO of 9A Climbing

Yet Tuscan is wary. “Basing R&D efforts on such incomplete research worries me,” he explains. “We don’t know what rubber they tested, and they only sampled nine gyms—including some Austrian ones known to be crowded and poorly ventilated.” Tuscan notes the widely used white rental shoe rubber—likely less abrasive—wasn’t tested (confirmed by Masset). “High-performance shoes are more abrasive, producing more RDCs. But 80% of climbers—especially in private gyms—don’t even use them.” He urges caution, not rushed reactions.

"Initially, it was the dust from the magnesia that we had to contend with. We soiled the filters so quickly that we had to change them two or three times a day. It was unmanageable." — Grégoire de Belmont, Arkose co-founder

But he must first verify the ACS ES&T Air study’s conclusions—not easy, especially given its apparent arbitrariness. "Basing my R&D efforts on such incomplete research feels dangerous," Tuscan sighs. "We don’t even know which soles they analyzed. They only sampled nine European gyms, several in Austria notorious for being overcrowded and poorly ventilated." Tuscan also notes the white soles commonly used in rental shoes—presumably less abrasive—weren’t analyzed (Masset confirms this). According to Tuscan, high-performance shoes worn by advanced climbers cause greater abrasion, releasing more RDCs—but they only represent a minority of gym climbers. Full of doubts, EB’s boss remains cautious.

Across the Alps, in the Dolomites, global climbing shoe giant La Sportiva also reacted quickly. Francesco Delladio, Product Manager, reached out to sole supplier Vibram, which contacted the University of Vienna (collaborating with EPFL on the study). Given Vibram’s usual reticence, Delladio expects limited feedback. Meanwhile, he calls for industry-wide unity to protect climbers' health.

Millions Invested in Air Renewal

There's no denying that the publication of the ACS ES&T Air study has shaken the climbing gym industry like never before. Already stressed by economic slowdown and the early signs of social unrest within their sector, private gym owners have intensified communication efforts and transparency initiatives. Many have issued statements, blog posts, or newsletters pledging the cleanliness and air quality of their facilities. Some, like Climbing District, even went as far as hiring a YouTuber to explain the scientific study and promote their own health policies.

In Paris, close to the iconic Sacré-Cœur, a climbing gym of a new kind opened its doors at the end of 2023. Vintage furniture, a gleaming restaurant, and a coworking area beneath a dome bathed in natural light all lead into a 1,200-square-meter climbing space… Welcome to Arkose Montmartre. Yet it’s another place entirely that Grégoire de Belmont, co-founder of the Arkose network, wants to show us. Behind a hidden door, giant machines hum loudly, surrounded by metal cabinets labeled with bold capital letters. This is the engine room ensuring air quality in one of France’s busiest climbing gyms.

The “engine room” at Arkose Montmartre © Vertige Media

Arkose’s management deliberately chose to oversize the ventilation system. Simply put, the franchise doubled ventilation standards (60 m³/h per climber instead of the legally required 30 m³/h). Thanks to this equipment, Grégoire de Belmont states confidently that he can renew “100% of the gym’s air three times per hour.” Implementing this standard across the network’s 30 gyms throughout Europe required significant investment—indeed, massive. “A machine like this costs €500,000 to purchase and €25,000 per year to maintain,” he reveals. Regarding the study, Belmont emphasizes he didn’t need it to worry about air quality in his gyms. “Initially, we were fighting against chalk dust,” Grégoire de Belmont explains. “It was extremely annoying, it got everywhere. Filters became clogged so quickly we had to change them two or three times daily. It was unmanageable.”

“I’m afraid the big players with deep pockets will impose new standards on smaller gyms like ours. So we have to be creative, work twice as hard, and invent new ways of doing things.” — Pierre Serin, owner of Solo Escalade in Toulouse

However, Belmont stresses that spending half a million euros on a dual-flow turbine alone won’t make all pollution problems vanish. Climbing gyms have become hybrid environments mixing numerous particles. The solution? Natural ventilation, rigorous cleaning (Arkose spends €1 million annually on cleaning alone), and restrictions such as limiting powdered chalk in favor of liquid chalk. Grégoire de Belmont admits zero risk doesn’t exist, but he remains convinced that his gyms remain far from a genuine health scandal.

Ingenuity’s Fine Particles

It’s the same story in Toulouse. After 30 years in the business, Pierre Serin has weathered numerous hygiene scares in climbing gyms—often justified. “Above all, I quickly identified powdered chalk as a major issue,” he says. “Anyway, we quickly noticed it in our smaller gyms. We’d go home with our nose hairs completely caked together!” Ever the resourceful independent, Pierre Serin experimented early. Back in 2003, he’d already pitched to Beal a prototype liquid chalk stick, drawing general laughter. “Now they sell tons of the stuff!” he jokes, smiling. “But the story isn’t over yet. To dry quickly, liquid chalk is loaded with alcohol. That opens your pores, and you’re injecting all sorts of nasty things directly into your bloodstream. One day that’ll come out.” According to Serin, gym managers will have no choice but to experiment under increased health scrutiny. “I’m worried about one thing,” he confesses. “I’m afraid the big players with deep pockets will impose new standards on smaller gyms like ours. So we have to be creative, work twice as hard, and invent new ways of doing things.”

Concretely? The Toulouse entrepreneur replaced carpet floors with tarps to prevent dust retention. He also removed wall friction as much as possible to limit shoe abrasion. And his latest innovation? “I sewed a piece of absorbent glove fabric onto a chalk bag. It absorbs sweat extremely well. You just wipe your fingers on it, like climbers naturally do, and voilà, no more chalk needed.” He continues: “But of course, people laughed at me again. Talking about this to climbers today is like mentioning chalk sticks 20 years ago... I think many innovations in climbing are hindered by cultural barriers.”

Precisely for this reason, the veteran climbing-gym owner welcomed the ACS ES&T Air study. “I think it broke down certain barriers,” he states firmly. “Now I think everyone wants to do better.” Concluding with a wink, he adds: “It’s good that this study pointed out something we used to sweep under the rug—no pun intended.”

All interviews conducted by Matthieu Amaré and Pierre-Gaël Pasquiou, unless otherwise noted.