Hot Baths Supercharge Heart, Immune System Better Than Saunas

EUGENE, Ore. — If you’re looking to boost your cardiovascular health without breaking a sweat at the gym, you might want to skip the trendy sauna sessions and head straight for a hot bath instead. A new study comparing three popular heat therapy methods found that soaking in hot water delivers more powerful health benefits than either traditional or infrared saunas.

Scientists at the University of Oregon put 20 healthy young adults through three different heating sessions and discovered that hot water immersion leads to the greatest thermoregulatory, cardiovascular, and immune responses compared to saunas. Wellness influencers have been touting expensive sauna treatments as the ultimate health hack, but taking a hot bath might be a cheaper, at-home way to achieve the same results.

The findings, published in the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, tackle the current heat therapy trend dominated by high-end sauna studios and infrared therapy sessions. Instead, the study shows that something as simple as a 45-minute soak in hot water creates more dramatic physiological changes than sitting in a traditional sauna or a far infrared sauna.

Comparing Three Types of Heat Therapy

Researchers designed their experiment to mirror how people actually use these heating methods rather than create artificial laboratory scenarios. Twenty participants, split evenly between men and women and with an average age of 24, underwent three separate heating sessions spaced at least a week apart.

Each session followed a different protocol. For hot water immersion, participants soaked up to their sternum (chest bone) in 104.9°F water for 45 minutes. The traditional sauna session involved three 10-minute rounds at 176°F (though actual measured temperature was 151°F) with 5-minute breaks at room temperature between sessions. Far infrared sauna participants sat for 45 minutes in temperatures that were set to start at 115°F and gradually increase to 149°F, though the actual measured temperature averaged 113°F.

Scientists monitored core body temperature every five minutes and measured heart function before, during, and after each session. They also collected blood samples to examine inflammatory markers and immune cell activity immediately after heating and again at 24 and 48 hours later.

Hot Water Wins

Hot water immersion increased participants’ core body temperature by an average of 1.98°F, while traditional sauna raised it by just 0.72°F, and infrared sauna caused virtually no increase at all. This temperature difference triggered a cascade of physiological responses that set hot water apart from its sauna competitors.

Heart rates jumped by 39 beats per minute during hot water immersion compared to 34 beats per minute in traditional saunas and 25 beats per minute in infrared saunas. Cardiac output, which is how hard your heart works to pump blood, increased by 3.7 liters per minute in hot water. This is significantly more than the 2.3 liters per minute increase in traditional saunas or the 1.6 liters per minute boost in infrared saunas.

Soaking in hot water also lowered blood pressure the most. Mean arterial pressure (the average pressure in arteries during a heartbeat cycle) dropped by 15 mmHg in the hot tub compared to just 4 mmHg in traditional saunas and virtually no change in infrared saunas. This mirrors what happens during moderate-intensity exercise, suggesting hot water immersion could serve as an alternative for people unable to engage in traditional physical activity.

How Hot Water Boosts The Immune System

Only hot water immersion triggered immune system changes. Participants showed increased levels of interleukin-6, an inflammatory marker that plays a beneficial role in the body’s adaptive response to stress. This same inflammatory response occurs after exercise.

Additionally, natural killer cells and certain T-cells increased 24 and 48 hours after hot water sessions. These immune cells help the body fight infections and potentially cancerous cells, suggesting that hot water immersion might provide lasting immune system benefits beyond the immediate session.

Why Hot Water is So Effective

Water conducts heat 24 times more efficiently than air, allowing for rapid and uniform heat transfer to the body. When you’re submerged in hot water, your entire body surface receives consistent heating, unlike saunas, where the air temperature varies and your body can cool through sweating. Being submerged in water reduces the body’s ability to cool itself through sweat evaporation.

Researchers also discovered important discrepancies between sauna settings and actual temperatures. When they measured actual temperatures inside commercially available saunas, they found the traditional sauna set to 176°F actually measured only 151°F with their research-grade instruments, while the infrared sauna averaged 113°F despite being programmed for higher temperatures. Many people using saunas aren’t experiencing the intense heat levels they think they are, potentially limiting the health benefits.

For people considering heat therapy as part of their wellness routine, a simple hot bath might be more effective than expensive sauna memberships. The study participants tolerated 45 minutes of hot water immersion well, though they did report feeling warmer and less comfortable than during sauna sessions.

The research also revealed that traditional sauna protocols with cooling breaks, common in Finnish sauna culture, might actually limit the therapeutic benefits by allowing core body temperature to drop between heating rounds. Continuous heating seems to be more beneficial for triggering the desired physiological responses.

“It can be a very peaceful, sometimes religious, sometimes cultural, and sometimes social experience,” says study author Christopher Minson from the University of Oregon, in a statement. “And I think those aspects contribute to the health benefits and are critically important.”

Still, the study focused on young, healthy adults who were recreationally active. Whether these findings apply to older adults, people with health conditions, or sedentary people has not been determined yet. Minson stresses the importance of medical clearance before beginning any heat therapy regimen.

“We want people to be smart and safe about it,” he adds. “We need to make sure that they are cleared by their physicians or others for heat therapy or for exercise, whether it’s mild to moderate walking or jogging or strength training. Then they’ll be fine to do heat therapy.”

Wellness trends come and go, but this research provides solid evidence that a hot bath at home can be a legitimate way to boost your health. For maximum cardiovascular and immune system benefits, science points toward the simple pleasure of a long, hot soak—no expensive spa membership required.