A team of scientists in Vienna have turned their attention to an unlikely pollution suspect: climbing shoes. These specialized shoes, prized for their grip and flexibility, have long been part of the climber’s toolkit. But now, it turns out they may also be a hidden source of toxic chemical exposure.
A new study published in ACS ES&T Air reveals that indoor climbing gyms across Europe contain unusually high concentrations of rubber-derived compounds (RDCs)—chemical additives used in high-performance rubber. The source isn’t the walls nor the mats, but the climbers’ own shoes.
The Pollution Source Nobody Saw Coming
The team, led by Anya Sherman and Thilo Hofmann from the University of Vienna, collected samples from gyms in Austria, France, Spain, and Switzerland. What they discovered was startling: the levels of certain rubber additives in climbing hall air and dust far exceed those found in homes, gyms, and even roadsides.
“We were familiar with the black residue on the holds in climbing gyms, the abrasion from the soles of our shoes. Climbers wipe it off to get a better grip, and it gets kicked up into the air,” she said.
Together with Thibault Masset from EPFL Lausanne, Sherman decided to investigate. They used a specialized device called an impinger, which mimics the way human lungs inhale and filter air, to collect airborne particles in nine bouldering gyms across Austria, France, Spain, and Switzerland.
They found rubber-derived compounds in every sample.
Among them were 6PPD, a chemical that preserves rubber but whose breakdown product has been linked to the death of salmon in rivers, and benzothiazole, a substance associated with higher bladder cancer rates in industrial workers.
The levels recorded weren’t just elevated—they were, in many gyms, comparable to the roadside air in major Chinese cities.
What Does This Mean for Your Health?
The precise health risks to humans are still being studied. But lab research and field studies paints a worrying picture.
Animal studies have shown that 6PPD-quinone—the breakdown product of the common tire additive—can cause lung inflammation, organ damage, and scarring. A recent study in China linked the chemical to respiratory damage in people, and children in high-exposure areas were more likely to suffer from infections like the flu.
While benzothiazole exposure in climbing gyms is likely far lower than in factories, it still raises questions. “It makes sense to act before we know all the details about the risks, especially with regard to sensitive groups such as children,” said Hofmann.
Sherman agrees. And while she’s still an avid climber, she’s urging caution and improvements. “This constructive cooperation should lead to the creation of the healthiest possible climbing hall environment, for example through better ventilation, cleaning, avoiding peak times and designing climbing shoes with fewer additives.”
Gyms are exposure hot spots
To understand the risks, the team estimated the daily intake of RDCs for both climbers and gym employees. The results show that daily exposure levels—especially for workers—can exceed those found near roads and industrial sites.
The researchers calculated exposure values of up to 48 nanograms per kilogram per day for employees. This is several times higher than known exposures from air pollution or contaminated household dust.
In comparison, “6PPD-quinone concentrations were higher than in most house dust samples collected around the world,” the authors noted. Employees, who spend more time in the gym than climbers, are especially vulnerable. These findings suggest climbing gyms may be under-recognized occupational exposure hotspots.
From Niche Hobbies to Mainstream Concerns
The findings are timely because they come at a time when climbing is becoming widespread.
Bouldering, a form of climbing without ropes or harnesses, has exploded in popularity. Sleek gyms have sprung up in urban centers, drawing everyone from office workers to Olympic athletes. In the U.S., about 1 in 20 people have tried indoor climbing. Roughly 20% of them are regulars.
That popularity makes the new findings rather urgent. The scientists behind the study emphasize they’re not sounding an alarm to stop people from climbing. Instead, they hope to spur action: better ventilation, materials reformulation, and more research.
“It is essential to switch to sole materials with fewer harmful substances,” said Hofmann. “Manufacturers are currently not sufficiently aware of the problem.”
For Sherman, the motivation is personal and professional. “I will continue to climb,” she said, “and I am confident that our research will contribute to better conditions in climbing gyms.”
