What the Heat Is Actually Doing: New Sauna Research, Read Honestly

Sauna is having a moment. Infrared blankets are all over social media, and every week somebody promises that 20 minutes of heat will fix your life.

We plan to offer sauna and cold plunge at MJM Betterment in the future. That’s exactly why we want to read the research straight, not sell it. So I went down the rabbit hole on what’s been published lately. Here’s what I found, including the parts that don’t make a good ad.

What one hour of heat does to a body

This year, researchers at St. Mary’s University presented a small pilot study as a conference abstract, not yet a full peer-reviewed paper (Nicolet, Enslow et al., International Journal of Exercise Science: Conference Proceedings, 2026). Eight healthy young adults lay for 60 minutes in an infrared sauna blanket set to about 75 °C. On another day, they lay in the same blanket switched off.

With the heat on:

Body temperature measured under the tongue climbed from about 36.8 °C to 38.2 °C. With it off, temperature didn’t change.
Participants lost about 1.3 liters of sweat, compared with 0.3 liters with the blanket off.
Diastolic blood pressure didn’t meaningfully change in either session.
By the end, people rated the heat close to the top of the scales. On a simple “how do you feel” scale, they landed on the unpleasant side.

The researchers’ conclusion is careful and worth repeating. The blanket produced “pronounced thermoregulatory and cardiovascular responses… consistent with the acute heat stress observed with more traditional heating modalities such as Finnish sauna.”

The key word there is stress. Heat is a real load on the body: your heart works harder, blood vessels near the skin open up to dump heat, and you sweat. A few of those responses overlap with light exercise, but that’s where the comparison ends. As the Finnish trial below shows, heat didn’t add to what exercise did.

And remember the sample size. Eight people, all around 20 years old. It’s a starting point, not a conclusion.

The heart research, and who it’s actually about

The best-known trial here is WAON-CHF, a randomized study at 19 hospitals in Japan (Tei et al., Circulation Journal, 2016). It enrolled 149 hospitalized patients with advanced heart failure. On top of their usual medical care, half got Waon therapy: 15 minutes in a far-infrared dry sauna at 60 °C, then 30 minutes of rest under a blanket, once a day for 10 days. Symptom class, 6-minute walk distance, and heart size on X-ray improved significantly only in the Waon group. But the trial’s main measure, a blood marker of heart strain called BNP, did not show a statistically significant difference between the groups. No serious adverse events were reported.

Two things matter more than the headline:

These were patients in medical settings under clinical supervision. This research is about cardiology care, not a spa.
One trial is not a verdict. It ran 10 days, in hospitalized patients, in one country, and its main measure missed. Nothing here means a sauna, including any MJM Betterment may offer someday, will help a heart condition.

The other side: when sauna added nothing

Here’s the study I’d want every sauna fan to read. A randomized trial in Finland, the home of the sauna, split 38 sedentary middle-aged adults into three groups for 8 weeks: exercise plus a 15-minute sauna afterward, exercise alone, or no change (Lee et al., Physiological Reports, 2025).

The researchers were measuring heart rate variability, a common marker of how the nervous system shifts between “go” and “rest.” Exercise moved some of those measures in a good direction. But adding sauna on top of exercise made no statistically significant difference on any of them.

That’s not a knock on sauna. It’s a reminder that the body doesn’t care about hype. Movement still does a lot of the heavy lifting, and heat is not a shortcut around it.

So what does this mean for someone coming home to their life?

Here’s why heat and cold matter to us anyway. It’s not because they fix anything. It’s because of what they practice.

When you sit in real heat, your body gets loud. Your heart speeds up, your skin burns, and every instinct says get out. You learn to breathe, stay calm, and choose when to leave. That’s a rehearsal for what reintegration asks of people: staying steady when old triggers make the body loud, and choosing the new response instead of the old reflex.

That’s the role we hope sauna and cold plunge will play at MJM Betterment once we offer them: a place to practice staying calm while uncomfortable, paired with community and reflection. Not a treatment, and not a substitute for medical care.

If you’re curious about heat right now:

Respect it as a stressor. It isn’t a nap. Hydrate, skip alcohol, start short, and get out if you feel dizzy, sick, or faint.
Talk with your clinician first if you have a heart condition, low or high blood pressure, a history of fainting, are pregnant, or take medications that affect heat tolerance. The same goes for cold-water plunges, which put their own sudden load on the heart.
Don’t skip the movement. In the Finnish trial, the exercise did the measurable work.
Notice what you do when it gets uncomfortable. That’s the real lesson.

Be Better. Not hotter. Better.

Sources

Nicolet J, Enslow B, et al. The Acute Physiological and Perceptual Responses to an Infrared Sauna Blanket: Towards Home-Based Passive Heat Therapy. International Journal of Exercise Science: Conference Proceedings, 2026 (conference abstract). https://digitalcommons.wku.edu/ijesab/vol2/iss18/142/
Tei C, et al. Waon Therapy for Managing Chronic Heart Failure: Results From a Multicenter Prospective Randomized WAON-CHF Study. Circulation Journal, 2016;80(4):827–834. https://doi.org/10.1253/circj.cj-16-0051
Lee E, Ketelhut S, Wiklund P, Kostensalo J, et al. Regular postexercise sauna bathing does not improve heart rate variability: A multi-arm randomized controlled trial. Physiological Reports, 2025;13(13):e70449. https://pmc.ncbi.nlm.nih.gov/articles/PMC12231185/

Education only, not medical advice. Talk with a qualified clinician about your own health.