New Finnish Study Challenges Global Sauna Norms: Humidity Is as Crucial as Heat for Health Benefits

Harvia and University of Jyväskylä research reveals that traditional Finnish 'löyly' (sauna steam) is a key driver of sauna's physiological effects, offering a more effective and pleasant experience than just dry heat.

MUURAME, Finland, July 21, 2026 /PRNewswire/ -- A groundbreaking study from Finland, the home of sauna, is set to redefine the global understanding of what constitutes an optimal sauna experience. Research conducted by Harvia, the global leader in sauna market, in collaboration with the University of Jyväskylä and the Finnish Institute of High-Performance Sport (KIHU), scientifically proves for the first time that humidity is an independent and powerful factor in delivering the physiological benefits of sauna, on par with temperature. The findings were published in the peer-reviewed journal Temperature.

The findings challenge the "hot and dry" sauna culture prevalent in many parts of the world and provide a scientific explanation for the traditional Finnish practice of throwing water on sauna stones – a practice known as löyly.

The study, the most comprehensive of its kind to simultaneously measure the sauna environment and the human body's response, found that both temperature and humidity independently increase heart rate and core body temperature. The average heart rate increase observed was 41.6 beats per minute; a cardiovascular response comparable to moderate-intensity exercise.

"For decades, sauna research has focused almost exclusively on temperature. Our study changes the conversation," says Timo Harvia, Chief Technology Officer at Harvia. "We now have scientific proof for what Finns have known instinctively for centuries: the steam from löyly is not just for comfort, it is a critical tool for regulating the sauna's health impact. This study explains why throwing water on the stones feels so good – it's actively enhancing the body's response. We are happy to share this knowledge with other researchers to advance a broader understanding of the health effects of sauna."

A new perspective for international sauna enthusiasts

This research has significant implications for global sauna cultures. In a wellness landscape increasingly focused on bio-hacking and measurable results, the study's finding that humidity independently raises core body temperature is crucial. The research shows that a traditional Finnish sauna with löyly is a highly effective way to achieve this key health marker.

In markets like Germany, where "combi" heaters with steam functions and ritualistic Aufguss ceremonies are popular, the study provides new insight. It demonstrates that the user-controlled, dynamic humidity created by traditional löyly offers a powerful, direct method to customize the sauna's intensity and physiological effect, potentially offering a more impactful experience than automated steaming.

The science of steam and a multitude of health benefits

The study revealed that the relative humidity in the sauna room was 6% among a group that did not throw löyly, whereas the group that threw löyly the most reached a relative humidity level of 59%. The 53-percentage point difference in relative humidity is significant and equals to almost 0.5 °C rise in core temperature. To unlock many of sauna's well-being benefits, the body typically needs to raise its core temperature by around 0.5–2 °C. Löyly is fundamental to achieving this efficiently, making it one of the defining elements of the authentic sauna experience.

These findings build upon a robust body of existing research that has documented the extensive health benefits of regular sauna use. With over 500 scientific studies conducted, sauna bathing has been proven to:

• Improve cardiovascular health by lowering blood pressure and enhancing circulation.
• Reduce the risk of memory diseases, with studies showing a reduction of over 60% in dementia risk for frequent users.
• Aid in muscle recovery and reduce pain by relaxing muscles and reducing inflammation.
• Strengthen the immune system and support respiratory health.
• Improve mental well-being by reducing stress and improving sleep quality.
• Contribute to a longer lifespan, with regular use linked to lower overall mortality.

About the study 

Fifty healthy adults participated in four 10-minute sauna sessions. The four saunas used different heater types: electric, wood-burning, gas, and hydrogen. All were set to approximately 75 °C, but participants were free to throw löyly as much or as little as they liked after the first two minutes of each session. Throughout, researchers precisely measured the sauna cabin's temperature and humidity at multiple points while simultaneously tracking participants' core body temperature, skin temperature, and heart rate. This dual-measurement methodology is a first in sauna science, providing an unprecedentedly clear link between the environment and the body's response.

Additional information about the study can be found here.

Further information: 

Timo Harvia, Chief Technology Officer, Harvia Plc. Interview requests of Mr. Timo Harvia are coordinated by Roosa Hytönen, tel. +358 505567825, [email protected]

Iida Laatikainen-Raussi, M.Sc., Corresponding Author, University of Jyväskylä, tel. +358 40 065 5816, [email protected]

About Harvia 

Harvia is one of the leading companies operating in the sauna market globally, as measured by revenue. Harvia's brands and product portfolio are well known in the market, and the company's comprehensive product portfolio strives to meet the needs of the international sauna market of both private and professional customers.

Harvia's revenue totaled EUR 198.9 million in 2025. Harvia Group employs over 700 professionals in Finland, United States, Germany, Romania, China and Hong Kong, Austria, Italy and Sweden. The company is headquartered in Muurame, Finland, adjacent to its largest sauna and sauna component manufacturing facility.

With a mission of "Healing with Heat," Harvia is dedicated to advancing the scientific understanding of sauna's health benefits through its research and innovation engine, Harvia Labs.

About the University of Jyväskylä (JYU)

The Faculty of Sport and Health Sciences at the University of Jyväskylä is Finland's only education and research unit specializing in sport sciences. It is an internationally significant scientific community that promotes physical activity and well-being.

About the Finnish Institute of High-Performance Sport (KIHU)

The Finnish Institute of High-Performance Sport (KIHU) provides scientific support for elite sports, along with research, development, and innovation in the field. KIHU utilizes research data, new technology, and innovations to create best practices for coaching and sports-related decision-making.

SOURCE Harvia