If you love ending the day with a sauna, hot tub, or soak in a hot bath—here’s something to celebrate: science officially has your back.
A 2025 study published in the American Journal of Physiology tested three popular heat therapies—hot-water immersion, traditional dry sauna, and infrared sauna—to see which one delivers the most health benefits.
And the winner? Hot water immersion—aka a hot tub or a hot bath—came out on top.
The Study: What They Did
Conducted at the University of Oregon, the study involved 20 healthy adults (10 men, 10 women) who each completed all three heat sessions spaced one week apart:
- Hot-water immersion (HWI): 45 minutes at 40°C (~104°F)
- Dry sauna: Three 10-minute rounds at 80°C with breaks
- Far-infrared sauna: 45 minutes at 45–65°C
Researchers measured changes in core temperature, heart performance, and immune activity before, during, and after each session.
Key Results: Why Hot Baths Work Best
1. Core Body Temperature Increase
- Hot bath: +1.1°C
- Dry sauna: +0.4°C
- Infrared: No significant change
That higher internal heat is crucial—it’s what activates most of the cardiovascular and immune benefits.
2. Cardiovascular Response (Cardiac Output)
- Hot bath: +3.7 L/min
- Dry sauna: +2.3 L/min
- Infrared: +1.6 L/min
Basically, your heart is doing a gentle workout—just from soaking.
3. Immune Activation
Only hot-water immersion increased key immune markers:
- Interleukin-6 (IL-6)
- Natural killer (NK) cells
- CD8+ T-cells (still elevated 48 hours later!)
So not only does your body warm up and circulate better—it also gets stronger at defending itself.
Why Water Beats Dry Heat
In a sauna, your body naturally sweats to cool down. But in hot water, heat is trapped—meaning your core temperature rises more and stays high longer. That’s why you feel so calm (and flushed!) after a hot bath. And now we know it’s not just a feeling—it’s a measurable, meaningful health response.
How to Recreate the Benefits at Home
The best part? You don’t need a fancy spa or home sauna to enjoy this. The exact health-boosting conditions used in the study can be recreated in a regular bathtub—as long as it’s hot enough and you stay in for 30–45 minutes.
My Top Product Picks for a Spa-Like Bath
(Affiliate links – I may earn a small commission at no extra cost to you)
- Bath Pillow
Extra Thick Bathtub Pillow for Head Neck and Back Support – lean back and relax fully (Amazon Canada | Amazon US)
- Epsom Salts with Essential Oils
Dr Teal’s Relax & Relief Soak – helps soothe sore muscles and uplift your mood (Amazon Canada | Amazon US)
- Bath Tray Caddy
Adjustable bamboo bath tray – Elevate your bathing experience with this bath tub tray that holds everything you need for a soothing soak (Amazon Canada | Amazon US)
- Mood Lighting
Floating waterproof LED lights – for that cozy spa atmosphere (Amazon Canada | Amazon US)
- Bubble Massage Mat for Bathtub
Portable Spa Bubble Bath Mat with Remote Control – this turns your regular bathtub into a bubbling spa. It’s air-powered, remote-controlled, and recreates that “hot tub effect” in your own tub. Great for circulation and relaxation—just like the study showed (Amazon Canada | Amazon US)
What About Cold Plunge?
The 2025 study didn’t include cold-water immersion—but don’t count it out!
Other research shows that contrast therapy (hot + cold) can boost circulation, reduce inflammation, and train your nervous system. So if you love ending your sauna with a cold shower—or jumping in a lake after a soak—you’re getting a different, but equally valid, kind of benefit.
But if you’re not ready for cold therapy yet? Hot water alone is powerful—as this study clearly shows.
Final Takeaway: Your Wellness Ritual Just Got Validated
Whether you prefer a spa soak, a gym hot tub, or a deep bath at home—this study confirms what we’ve felt all along: heat heals.
Hot water boosts your heart, your circulation, your immune system, and your mood. And it’s one of the most accessible self-care tools out there.
So fill that tub, hit that 40°C mark, and give yourself permission to relax—knowing your body is soaking up every second.