Human Heat Tolerance Lower Than Previously Believed: Study Finds - Video

A study from the University of Ottawa's Human and Environmental Physiology Research Unit (HEPRU) has confirmed that the limits for human thermoregulation are lower than previously thought. The findings are published in Proceedings of the National Academy of Sciences.

The research highlights the urgent need to address the impacts of climate change on human health. The study found that many regions may soon experience heat and humidity levels that exceed the safe limits for human survival.

Utilizing a widely used technique known as thermal-step protocols, researchers exposed 12 volunteers to various heat and humidity conditions to identify the point at which thermoregulation becomes impossible. Participants were subjected to extreme conditions, 42°C with 57% humidity, representing a humidex of approximately 62°C. “The results were clear. The participants’ core temperature streamed upwards unabated, and many participants were unable to finish the 9-hour exposure. These data provide the first direct validation of thermal step protocols, which have been used to estimate upper limits for thermoregulation for nearly 50 years”, says Meade former Senior Postdoctoral Fellow Ottawa's Faculty of Health Sciences.

Reference: R.D. Meade, F.K. O’Connor, B.J. Richards, E.J. Tetzlaff, K.E. Wagar, R.C. Harris-Mostert, T. Egube, J.J. McCormick, & G.P. Kenny, Validating new limits for human thermoregulation, Proc. Natl. Acad. Sci. U.S.A. 122 (14) e2421281122, https://doi.org/10.1073/pnas.2421281122 (2025).