Heat therapy may feel similar on the surface, but the body does not experience every warm environment in the same way. A new study from the University of Oregon compared hot water immersion, traditional sauna use, and far-infrared sauna sessions to see how each affects the body's internal systems.
Researchers at the Bowerman Sports Science Center worked with 20 healthy adults, split evenly between men and women, and monitored changes in core temperature, heart rate, blood pressure, cardiac output, and immune markers across multiple sessions.
Water and air create different heat loads
The study found that all three methods raised body temperature, but hot water immersion produced the strongest effect. In water, the body loses its main cooling tool: sweat evaporation. That means heat builds up more quickly than it does in dry sauna conditions, where sweat can evaporate and help regulate temperature.
As a result, hot tub sessions led to a larger rise in core temperature, a stronger cardiovascular response, and a more noticeable shift in immune activity. The researchers observed changes in inflammatory cytokines and immune cell levels only after water immersion.
Traditional and far-infrared saunas also increased body temperature and circulation, but their effects were less intense than the hot water condition. According to the team, these heat responses resemble some of the body's reactions during moderate aerobic exercise, even though the person remains at rest.
Why the findings matter
The results offer a clearer picture of how passive heat therapies work and may help guide future wellness and clinical research. For people who cannot always exercise because of mobility limits or injury, controlled heat exposure could become a useful supportive tool.
Still, the study focused on short-term responses in young, healthy adults, so it does not replace the proven benefits of physical activity. The authors also note that people with heart or blood pressure concerns should seek medical guidance before regular heat sessions.
By showing that sauna and hot tub use are not biologically identical, the research opens the door to more personalized heat-based wellness strategies that could shape future recovery and health routines.