I love our hot tub. Our son loves his dry sauna. And many of my patients love their infra-red sauna. Last week I wrote about the benefits of heat therapy related to the heat shock proteins. But I’ve always wondered, is one heat therapy better than another? I just got my answer.
A groundbreaking study published in AJP Regulatory, Integrative, and Comparative Physiology (June 2025) by Jessica Atencio and colleagues offers some clear answers. This study directly compared three popular forms of passive heat therapy – hot water immersion (HWI), traditional sauna (TRAD), and far-infrared sauna (FIR) – to see how each impacts body temperature, cardiovascular function, and immune system activity.
The trial involved 20 healthy adults (10 men and 10 women, average age 24), who each underwent all three heating sessions in random order, with a one-week break between each. The three sessions were: a 45-minute soak in hot water at 104.9°F; three 10-minute rounds in a traditional sauna at 176°F ; and a 45-minute exposure in a far-infrared sauna at 113–149°F. Researchers monitored changes in core body temperature, heart function, inflammatory cytokines, and key immune cell counts before, during, and up to 48 hours after each session.
So which method came out on top? When it comes to raising core body temperature, hot water immersion delivered the most significant boost – about 2°F on average, while the traditional sauna increased it by a modest 0.7°F. The far-infrared sauna barely moved the needle, producing negligible changes in core temperature. This matters because raising core temperature appears to be a critical trigger for downstream health benefits, including improved circulation and immune activation.
From a cardiovascular standpoint, hot water immersion again stood out. It increased cardiac output (the amount of blood the heart pumps per minute) by 3.7 liters—more than traditional sauna (2.3 L/min) and far-infrared sauna (1.6 L/min). While not as intense as exercise, this increased workload for the heart mimics moderate physical activity, offering a potential substitute for those unable to engage in vigorous workouts.
But perhaps the most fascinating difference showed up in immune system activity. Only hot water immersion led to a measurable increase in interleukin-6 (IL-6), a short-lived inflammatory marker that plays a key role in immune signaling. In addition, levels of natural killer (NK) cells and CD8⁺ T cells, both critical for fighting infections and cancer, rose significantly 24 to 48 hours after the hot bath. Neither the traditional nor infrared saunas produced these immune changes.
My Hot Tub Rules!
In short, this study shows that not all heat therapies are created equal. Hot water immersion offers the most robust physiologic and immune response. Its ability to rapidly raise core temperature, increase blood flow, and mobilize immune cells makes it a powerful tool for health optimization. Traditional saunas still have value, especially for cardiovascular support and relaxation, but their effects are gentler and more gradual. Infrared saunas, while popular for their comfort and perceived detox benefits, showed minimal impact in this head-to-head study.
So what does this mean for your wellness routine? If you’re aiming for maximum benefit, whether it’s improved immunity, heart health, or simply feeling energized, then a 30 to 45-minute soak in hot water around 104-106°F may be your best bet. Consider using a deep tub or hot tub 2–3 times per week. Be sure to stay hydrated, listen to your body, and rest for at least 10–15 minutes afterward. For those who prefer saunas, a traditional sauna session of 15–30 minutes at 175-195°F can still deliver valuable benefits, especially when practiced regularly.
Keep in mind that passive heat therapy isn’t for everyone. People with cardiovascular conditions, heat sensitivity, or pregnancy should consult a healthcare provider before beginning. And regardless of modality, the basics matter – stay hydrated, cool down gradually, and don’t overdo it early on.
Author
Scott Rollins, MD, is Board Certified with the American Board of Family Practice and the American Board of Anti-Aging and Regenerative Medicine. He specializes in bioidentical hormone replacement for men and women, thyroid and adrenal disorders, fibromyalgia and other complex medical conditions. He is founder and medical director of the Integrative Medicine Center of Western Colorado (www.imcwc.com) and Bellezza Laser Aesthetics (www.bellezzalaser.com). Call (970) 245-6911 for an appointment or more information.
