Exploring the science behind the power of heat as saunas grow in popularity across Ireland

As sauna culture continues to grow across Ireland, Gemma Fullam meets journalist Bill Gifford, whose new book uncovers the science behind the power of heat

Sat, 21 Mar, 2026 - 02:00

Gemma Fullam

It was a bitterly cold winter in Salt Lake City, Utah, when Bill Gifford first began using the “crap” sauna in his gym. The journalist and writer had been going through a tough time and craved “15 minutes a day of peace and comfort”, which the sauna’s warm, dark, quiet interior provided.

“It felt like an embrace,” says Gifford, who “felt like a new man” after the daily quarter-hour of heat, followed by a 15-second blast under the cold shower. That mood boost set him on a deep dive into the health benefits of heat, which he’s documented in Hotwired: How the Hidden Power of Heat Makes Us Stronger.

Heat gets a bad rap these days, most often appearing in the same sentence as ‘deadly’ (as in heatwaves), ‘extreme’ (as in climate change), and ‘rising’ (as in temperatures). We’re bombarded with ways in which heat is destroying our planet and killing us in the process. Humans and heat don’t mix, right? Wrong.

“Heat,”Gifford says, “is not just the devil, it also has some angel to it.” Not only is heat good for us, it’s an environment in which we were designed to thrive. Modern life, with its air conditioning and office jobs, has dulled our resilience and our ability to adapt to heat — but by reintroducing targeted heat stress and periods of sweating, we can reclaim it.

“Sweating is magical. Sweating helped us go from the middle of the food chain to the top,” Gifford says, explaining that the evolution of humans’ ability to regulate body heat through sweat helped us segue from prey to predator, enabling us to thrive as a species.

Sweating and heat go hand in hand. “Heat can be a powerful tool if it’s used safely and wisely for a specific reason,” Gifford says. The idea that heat could be healing was the jumping-off point for his journey of discovery, and he began it with where he had found solace: the sauna.

Sauna culture has exploded in Ireland since the pandemic, possibly because during those dark days people were craving the same things Gifford sought: peace and comfort. In Finland, where sauna is deeply embedded in the culture, the sauna is known as ‘the poor man’s pharmacy’.

“It was interesting going from the United States, which very much has an influencer-driven culture that’s all about the health benefits of sauna, to Finland, where it’s just a part of life,” Gifford says. “That was really eye-opening.”

Finnish saunas have etiquette and customs but no “hard and fast rules”, he says. “It’s much more free-form.”

You can stay in as long, or as little, as you like, cold plunging is optional, people are nude, and there’s often alcohol and always lots of chat. That laissez-faire philosophy of sauna-ing is one to which Dan O’Connor subscribes. O’Connor is the co-founder of The Hot Box, which had its genesis in a DIY sauna he helped his friend Liam Irwin build in his parents’ garden during the pandemic. Like Gifford, O’Connor’s experience of saunas had been limited to the gym variety but a visit to Shirley Fitzpatrick’s Bosca Beatha wild sauna in Wicklow opened his eyes to what a true sauna experience could be.

“Myself and Liam left feeling euphoric,” he recalls. “[We walked] away absolutely elated… they call it sauna-high.” They launched The Hot Box in Bective, by the River Boyne, with a mobile sauna built on a cattle trailer. They then brought a third friend, Luke Williams, on board, went to Finland, Latvia, Lithuania, and Estonia to get inspiration for expansion, and haven’t looked back since.

“Our purpose is to give ordinary people an extraordinary feeling,” O’Connor says. “It’s like, ‘Just come, take a load off for a little while; I guarantee you it will work.’ The benefits are great but we don’t want to go down the rabbit hole of becoming too specific of how long you should stay in a sauna, how long you should stay in a plunge pool. Staying as long as you want or as little as you want, that’s entirely up to you.” It’s a very Finnish approach.

While there’s no denying the beatific buzz that comes from a sauna session, is there actual science behind the steam? “The most surprising thing to me was the fact that targeted heat therapy has an effect on depression,” says Gifford. He volunteered for a clinical trial in Colorado during which he was heated to fever temperature, followed by a cold plunge. The aim was to reset his ‘inner thermometer’ — a 20,000-person study found that severely depressed people “run hotter” (and also tend not to sweat very much) — and, by doing so, banish his depression (and help him survive the Hotter’N Hell Hundred, a Texas bike race that’s as insane, and blisteringly hot, as it sounds).

Gifford says he was “moderately depressed” before the “horrible” experimental treatment but “at the end of it, it felt like it was a new day”.

He was still feeling the benefits three weeks later. (He also aced the bike race.) Most of the participants had significant improvement in their depressive symptoms after a single session, with effects lasting up to six weeks. The trial is ongoing.

You don’t have to cook yourself like a rotisserie chicken to get the mood-boosting benefits of heat therapy, though. In fact, you don’t even need to go to the sauna. A hot bath will do just as nicely.

“Hot-water bathing is just as healthy as sauna use, maybe even more so, because you get more of a direct heat transfer, so your core temperature increases,” Gifford explains. “A lot of the health benefits are related to a slight increase in your core body temperature.”

The heat gives your heart the equivalent of a cardio workout, improves circulation, and lowers blood pressure, while at a 38.5C body temperature, stress-resistant heat shock proteins are activated, which “keep your DNA from decaying and clear out waste products and all that kind of stuff”.

Gifford adds: “In fact, there was a study in Japan that found that people who take hot baths regularly had a similar reduction in heart attacks, all-cause mortality, and heart disease as people who used Finnish saunas regularly.”

Hot water is good but Gifford discovered that cold isn’t the holy grail of wellness people think it is.

“The science around heat, and heat as a therapeutic tool, is much stronger than the science around cold,” he says, adding that the studies to date on cold-water immersion have been small scale and, he says, often shaped by researchers hoping to find a positive effect.

“I think the benefits are a bit oversold,” he continues. “Especially if you’re talking about using [cold immersion] as a tool for athletes for recovery. If you do a strength workout and then hop in a cold plunge, you’ve just stopped any muscle adaptation, any muscle growth that you might’ve hoped for from your strength workout.”

A large study in the Netherlands that had a percentage of participants run a cold blast at the end of their shower found that “the benefits weren’t huge”, although those people did miss fewer days at work. Interestingly, Gifford says, the cohort who were assigned the cold blast kept doing it after the experiment concluded. “So some people really find it compelling and I think it gives you a mental charge. It can boost your mood if you’re coming into it in the right frame of mind.”

The jury is out, especially for women, he says, and that applies to heat as well as cold. A Finnish study that looked at hormone changes in women before and after sauna sessions found that a particular stress pathway was activated much more in women than in men. Is that a bad thing? “I think it depends,” says Gifford, reiterating: “It’s more stressful.”

It’s not one size fits all, is what he’s saying. When it comes to heat or cold, you need to listen to your body and do what feels right for you. It’s worth mentioning that Finnish saunas are much hotter than the average Irish sauna. Finnish saunas are all about the löyly: steam, and clouds of it.

“Old-time Finns thought the steam carried spirits,” Gifford says, “and if you see the way the steam comes up off the rocks, travels around the room, it’s almost like a living thing.”

That transfer of heat to skin in the sauna is, Gifford thinks, the “sensation that the Finns crave”. He adds: “And I think that’s the sensation that is cool about sauna. That’s the drug.”

It’s a drug that Irish people can’t get enough of. “What surprised us is how mad people are for saunas and cold plunges,” O’Connor says. “It just blew up. Now, a lot of people are substituting going out on a Friday or Saturday night for going to the sauna. It’s become an absolute place of socialising and meeting new people.”

Gifford doesn’t go to his sad gym sauna anymore; he’s got a neighbourhood place that is “basic but great”. He’s gone from a self-confessed “winter guy” to one who has “no problem” riding his bike on a sweltering summer day in Utah. Sweating has given him superpowers. His biggest takeaway from his heat odyssey?

“If you lean into some discomfort, you learn that you can do a lot more than you think you can. You can exceed your own self-imposed limits.”