Sauna humidity boosts heart rate and core temperature more than heat alone

A study by the University of Jyväskylä and the Finnish Institute for Sport and Health Sciences KIHU has found that higher humidity in saunas increases heart rate and core body temperature more than temperature alone. The research, which measured humidity for the first time in detailed sauna studies, suggests that people may gain similar health benefits at lower temperatures if humidity is high.

The study involved 69 volunteers who spent 10 minutes in four different types of saunas—wood-fired, electric, hydrogen, and gas-heated—while researchers tracked their core temperature and heart rate. Participants began throwing löyly (steam) after two minutes. The physiological explanation is simple: sweat cannot evaporate from skin in humid conditions, preventing the body from cooling normally.

Researcher Iida Laatikainen-Raussi, a regular sauna user herself, said the findings confirm what many Finns intuitively know. “Humid air feels more comfortable in the sauna, and the heat feels different when it’s more humid,” she said. While the study did not measure long-term health effects, it supports the idea that regular sauna use with higher humidity could produce benefits similar to those reported in earlier studies, such as lower blood pressure and reduced mortality risk.

Laatikainen-Raussi noted that sauna use raises heart rate and core temperature similarly to brisk walking, even though muscles remain passive. She hopes the findings will encourage people abroad to adopt the Finnish practice of throwing löyly, which is less common outside Finland.

Future research will focus on identifying the most comfortable sauna conditions and refining understanding of how sauna use affects health.