The Science Of Sweat, Saunas & Stress: Heat Makes Us Stronger
Heat is having a moment. Saunas are popping up everywhere, from boutique wellness studios to backyard barrel saunas to the steam room at your local gym that suddenly has a waitlist. But unlike some wellness trends that come and go, this one is backed by decades of compelling research.
I recently sat down with Bill Gifford, veteran science journalist and author of the new book Hotwired: How the Hidden Power of Heat Makes Us Stronger, on the mindbodygreen podcast, to find out what happens when we stop running from discomfort and start embracing the heat.
The Finnish sauna culture
Finland is known as a hotspot of sauna culture. Nearly every home in Finland has a sauna, they actually outnumber cars in the country. So I was surprised when Gifford told me that the Finns don't really think about saunas as a health practice.
"The sauna was akin to a bathtub. It's where you went to get clean. And it just happened to be that each person couldn't have an individual sauna," Gifford told me. "And it was a weekly thing, or every few days, where you would heat up the sauna and everybody would come in and get clean."
Americans tend to turn everything into a biohack, so we want concrete numbers for how long and how often we should sauna. But the Finns aren't obsessing over protocols or timing their sessions with stopwatches. They're not trying to optimize anything. They're just enjoying the heat.
And yet—or maybe because of—this relaxed approach, Finland has some of the most compelling research on sauna benefits in the world. A Mayo Clinic review found Finnish sauna bathing to be associated with a reduced risk of cardiovascular disease, high blood pressure, neurocognitive conditions, pulmonary diseases, and even mortality.
What happens when you heat up
Some people simply enjoy the feeling of their body detoxing in the heat, while others can't stand it. But Gifford explained to me exactly what it is about heat stress that makes it so good for your body, other than the feeling many people enjoy
When you expose your body to heat, your heart rate accelerates as your body works to maintain temperature homeostasis. Blood surges beneath the surface of the skin as your body tries to radiate heat outward. Your blood vessels dilate, and you begin to sweat. This produces a cardiovascular and vascular benefit similar to moderate-intensity exercise.
With repeated heat exposure, your body begins to adapt to the heat. Plasma volume expands, so your body learns to begin sweating sooner and more efficiently. You will also start producing more red blood cells, increasing hemoglobin and oxygen-carrying capacity, which is a adaptive response as altitude training.
Some athletes who have to compete in warm weather will actually train their bodies to function better in the heat, so they can develop these adaptations before they are on the field or running the track.
The mental health connection
One of the most surprising pieces of sauna research? The solid evidence of a mental health benefit from heat.
In his work, Gifford stumbled across a study that found people who regularly went to hot yoga for eight weeks experienced a significant decrease in depression symptoms.
This may connect back to why saunas were first popularized in Finland and the surrounding areas, where they experience long, cold and dark winters. Sweating it out not only warms up their bodies, but also lifted their moods.
For those of us dealing with the chronic stress of modern life, this feels significant. A practice that's been around for thousands of years might offer something our anxious brains desperately need.
Heat vs. cold: A contrarian take
Given all the hype around cold plunges, I had to ask: Which is actually better, heat or cold? Gifford's answer surprised me.
"The science of cold exposure and cold water immersion is really not as robust as the science around heat."
Cold exposure isn't useless. He acknowledges that cold can reduce inflammation, improve recovery, and provide a powerful mental challenge. But he specifically advises against cold plunging after a workout, which can actually hinder muscle growth.
He also suggests being careful about hot-cold contrast therapy. If you are going back and forth between a cold plunge and a sauna, make sure to spend adequate time cooling off. Even if your skin feels cold after a few minutes in the cold plunge, your core temperature will still be raised.
How to start sweating
The idea of spending 20 minutes in a sauna may not sound appealing to you right now, but one thing I learned from our conversation is that heat tolerance makes us stronger and more resilient.
"Sweating is our superpower," Gifford explained, but in the climate-controlled world we live in, our bodies have forgotten how to deal with the heat.
The good news? Heat adaptation comes back relatively quickly. Here's what he recommends for someone who wants to incorporate more heat into their life:
- Start where you are. You don't need a fancy infrared sauna or Finnish smoke room. A hot bath or the steam room at your local gym will work just as well.
- Build up gradually. If you're new to heat exposure, start with shorter sessions and work your way up. Try to stay in the sauna for a few minutes past when you begin to feel uncomfortable.
- Embrace the discomfort. This is key. The benefits come from the stress response, which means you need to actually get hot.
- Listen to your body. If you feel dizzy, nauseous, or unwell, get out. Heat exposure should be a bit of a challenge for your body, but not dangerous.
- Stay hydrated. Drink plenty of water before and after. Even if you're not a big sweater, your body will need to replenish.
The takeaway
What stayed with me most from my conversation with Bill Gifford wasn't any single study or protocol. It was bigger idea behind his book.
"There's value in leaning into discomfort—and leaning into the thing you think you don't like," he says.
The sauna, in this light, is more than a health practice. It's a reminder that growth happens at the edges of our comfort zone. That sometimes the thing we're avoiding—the heat, the sweat, the temporary discomfort—is exactly what we need.