In the latest video from MedCram, Dr. Seheult discusses the differences and advantages of using hot tubs, traditional saunas and infrared saunas.
Which Raises Core Body Temperature Best: Hot Tubs, Traditional Saunas, or Infrared Saunas?
In recent years, interest in passive heat therapies—like hot tubs, traditional saunas, and infrared saunas—has grown tremendously. While many people use these for relaxation or recovery, there’s increasing scientific interest in how these modalities affect core body temperature and, in turn, influence physiological processes such as cardiovascular function and immune responses. A new study published in the American Journal of Physiology tackled this question head-on, comparing the effects of these three heat therapies on thermoregulation, cardiovascular strain, and immune markers.
The study design was robust. It involved 20 healthy young adults (10 male, 10 female), each of whom underwent all three heating modalities—hot water immersion (HWI), traditional sauna (TRAD), and far-infrared sauna (FIR)—separated by at least one week in a randomized order. The researchers tracked a range of markers including core body temperature, heart rate, sweat loss, blood pressure, and immune cell counts. Importantly, each participant acted as their own control, which helped account for individual differences in heat tolerance or physiology.
Hot water immersion involved 45 minutes in a tub set at 40.5°C (104.9°F), with participants submerged up to their mid-sternum. Traditional sauna sessions were broken into three 10-minute intervals at a set temperature of 80°C (176°F), with 5-minute breaks between each. However, actual measured temperatures revealed that the sauna only reached around 66°C (150°F), a significant deviation from the intended heat. Similarly, the infrared sauna was set to reach 57°C (134.6°F), but actual temperatures measured only around 45°C (113°F), raising questions about how accurately consumer saunas reflect true conditions.
Results showed that hot water immersion was the most effective method for raising core body temperature. It elevated core temperature well above the 38°C (100.4°F) threshold associated with triggering beneficial immune responses, such as increased interferon production (though this specific marker wasn’t tested in the study). In contrast, traditional and infrared saunas did increase core temperature, but to a lesser degree—with infrared sauna showing the least effect.
Skin and Body Temperature
Skin temperature and mean body temperature (a combination of core and skin temperature) also varied across modalities. Traditional sauna produced more variability due to the in-and-out design of the session, while hot water immersion resulted in a more steady increase. The traditional sauna outperformed FIR in raising skin temperature but didn’t match HWI for core temperature elevation.
Cardiovascular response
In terms of cardiovascular responses, hot water immersion caused the greatest increase in heart rate and cardiac output. This is likely due to the vasodilation caused by elevated body temperature and the physical effects of water pressure, both of which increase circulatory demand. As expected, mean arterial pressure dropped more during HWI, suggesting it may be especially useful in improving vascular function. Stroke volume (the amount of blood pumped per heartbeat) also increased most with HWI.
Immune System effects
When it came to immune system effects, changes were more subtle. The study looked at inflammatory cytokines like IL-6, IL-1β, and TNF-α. Of these, only IL-6 showed a statistically significant increase, and only in the hot water immersion group. Similarly, changes in immune cell populations like CD4+, CD8+, and natural killer (NK) cells were only notable in HWI, particularly with a rise in CD8+ cells and NK cell markers 24 hours after the session. Traditional and infrared saunas did not lead to significant immune cell changes.
The researchers noted some important caveats. The study focused on acute responses in young, healthy, and recreationally active individuals. This means the results may not generalize to older adults or people with chronic diseases. In fact, the researchers suggest future studies should explore how these modalities affect different populations, especially those unable to exercise, as passive heating could serve as an alternative therapy.
Interestingly, the authors also highlighted the economic and practical advantages of hot tubs. While saunas may be more expensive or less accessible for some, hot water immersion might offer a simpler, more cost-effective option for achieving similar—or even superior—benefits, at least in terms of body temperature and cardiovascular strain.
As a final note, the study doesn’t discount the potential non-thermal benefits of infrared saunas. Although FIR underperformed in raising core temperature, there’s emerging evidence that infrared light itself may have unique effects on mitochondrial function, oxidative stress, and energy metabolism—benefits that weren’t measured in this study. So, while hot water immersion may be the most effective in acutely raising core temperature, each modality may have its own unique therapeutic niche.
This head-to-head comparison adds important context for anyone looking to use heat therapy for health. If your goal is to raise core body temperature and stimulate cardiovascular and immune responses, hot water immersion may be your best bet—at least in a single-session context. But when considering the broader benefits of heat therapy, including relaxation, mitochondrial health, and long-term adaptation, all three methods may still have value depending on your needs and resources.
LINKS / REFERENCES:
Comparison of thermoregulatory, cardiovascular, and immune responses to different passive heat therapy modalities (American Journal of Physiology) | https://journals.physiology.org/doi/e…