Hot Baths, Saunas, and Why Heat Therapy Works Like Exercise.

If you’ve followed my writing for a while (or indeed if you know me), you’ll know I’m always singing the praises of sauna use (see my previous blog article). And now, even more research is backing up what I’ve been saying all along: using heat — whether in a sauna or a hot bath — can mimic some of the same cardiovascular and immune benefits as moderate exercise.

This is good news if you don’t always have time for a workout, if you’re injured, or if you just want another way to support your healthspan and longevity. Let’s dive into the latest findings.

Heat as “Passive Exercise”

A new study compared three types of passive heat therapy:

• Hot water immersion (a bath at 40.5℃ / 105℉ for 45 minutes)

• Traditional sauna (80℃ / 176℉ for 3 x 10 minutes, with short cooling breaks)

• Infrared sauna (46–65℃ / 115–149℉ for 45 minutes)

The results were fascinating.

What They Found

Hot water immersion (the humble bath!) was the strongest cardiovascular workout of all.

• Blood pressure improved by 14 mmHg

• Heart rate increased by 39 bpm

• Cardiac output rose by 3.7 L/min

It also stimulated the immune system: natural killer cells and cytotoxic T cells were boosted for up to 48 hours, and IL-6 (a beneficial pro-inflammatory molecule linked to exercise) was elevated.

Traditional sauna came next.

• Heart rate rose by 34 bpm

• Cardiac output by 2.3 L/min

• Blood pressure reduced by 4 mmHg

Infrared sauna was the mildest.

• Heart rate +26 bpm

• Cardiac output +1.6 L/min

• Blood pressure down by just 1 mmHg

  
  

Why the Difference?

Heat works because it raises your core body temperature. The higher it goes, the more the body adapts — cardiovascularly, hormonally, and immunologically.

Hot water conducts heat more efficiently than air, so your body warms up more deeply in a bath than in a short sauna session. That’s why the bath had the strongest effects in this study.

But — and this is important — most real-world sauna users stay in longer than 10 minutes at a time. With a 20–30 minute traditional sauna session, you’d expect to see stronger results than those captured here.

Why Heat Helps Us Age Well

Heat exposure, like exercise, is a stressor that teaches the body to adapt. Benefits include:

• Cardiovascular fitness: lower blood pressure, improved blood vessel function

• Immune resilience: increased natural killer cell activity

• Stress balance: improved heart rate variability, nervous system regulation

• Hormone + brain support: increased growth hormone, BDNF (linked to cognition), and those blissful beta-endorphins that improve mood

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In short: you feel better now, and you build resilience for the future.

My Takeaway

You don’t have to choose “the best” method — sauna, infrared, or bath. The key is getting hot enough, for long enough, often enough.

• Hot bath: aim for 30–45 minutes at a comfortably hot (but safe) temperature

• Traditional sauna: 20–30 minutes at higher heat, 2–5 times a week

• Infrared sauna: longer sessions, ideally 40–45 minutes

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Personally, I still love the traditional sauna because of the decades of research linking it to lower risk of heart disease, dementia, and overall mortality. But if you don’t have access to one, a hot bath is an excellent alternative — and much more achievable for most people at home.

And let’s not forget — beyond the science, baths and saunas are deeply restorative rituals. They create time to pause, reflect, and reconnect with yourself, while your body does the clever work of adapting and healing.

Final Thought: Whether it’s a bath, sauna, or even a hot tub, think of heat as an ally in your self-care routine — one that supports your heart, immunity, and longevity in ways that mirror exercise.

References

Atencio, J.K., Reed, E.L., Needham, K.W., Lucernoni, K.M., Comrada, L.N., Halliwill, J.R. & Minson, C.T., 2025. Comparison of thermoregulatory, cardiovascular, and immune responses to different passive heat therapy modalities. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 329(1), pp.R20–R35.