KIRKWOOD, Mo. —

Touted for pain relief, cellular detox, cardiovascular improvement, lowered blood pressure and anti-aging, infrared saunas are celebrity-approved and gaining popularity.

But the spa treat is not without detractors who have medical degrees and reason for suspicion.

Traditional dry saunas heat the room, which in turn heats the occupants of said room. Moderate to intense sweating ensues as temperatures rise and promoters love to exclaim that this helps “flush toxins out of the body” as well as increase the heart rate. Studies show that this can provide a variety of benefits.

Hot not your thing? Try cold therapy instead.

A long-term study of sauna-loving populations in Finland and Japan show substantial decreases in risk for fatal heart disease when they enjoyed two or more days a week in a sauna. And, yes, the study determined that it wasn’t because healthier people were predisposed to prefer saunas.

Infrared saunas boast some of the same benefits, but because of the type of heat, there are also a few precautions.

Infrared delivers heat via electromagnetic radiation, which most of us readily associate with microwaves, although this is within the normal light spectrum. Infrared heat raises the temperature of the body without heating the room where that body is sitting. This means that the experience can feel less intense and stifling. It can be harder for people to gauge when they are overheating.

“I keep a binder of all the studies I can find to share with clients,” says Stacy Sullivan of Sol Sweat, a company offering private 40-minute infrared sauna sessions in Kirkwood. “I do it myself (she does as many sessions a week as she can sneak in), and I am very concerned about safety and comfort, which is why I let (the clients) control the temperature.” Sullivan also sells portable body-length, infrared heating pads.

One to two people can book a 40-minute session in a roomy, private booth within a private room with access to Netflix and music channels for $40 to $60 a session. There is color therapy lighting and specialized infrared programs of wavelength recipes to stimulate detox, weight loss or treat inflammation that can also be individually selected.

And yes, the science is a little murky on all of that, but many report some basic benefits.

“It just feels really good,” said Frances Pleimann, 29, of Kirkwood. “I use traditional saunas, and this just feels more pleasant. The heat is not as intense, and I like to max out the temperature.”

The saunas can provide more than 150 degrees of heat. Pleimann is a regular, coming at least once a week since Sol Sweat opened in November. She said that she considers the sauna a preventive measure of self-care and she’s not worried about any negative effects.

“That makes sense that some people might enjoy the simple pleasure of warmth and relaxation,” said Dr. Joel Schlessinger, a dermatologist in Omaha, Nebraska, who contributes to RealSelf, an online community for patients to ask questions about cosmetic treatments, wellness products and physicians.

But he maintains that limited, if any, exposure is best. He didn’t recommend an ideal time to stay in a sauna because he said there are too many unknowns when it comes to infrared light. There has yet to be a definitive peer-reviewed scientific study of the technology, so for now, he’s not a fan.

And yes, you’re getting infrared rays any time you feel warm from the sun. But anyone with health concerns should consult a doctor.

Infrared light has been linked to adverse eye health. And some people don’t have the health to tolerate the heat, even though it “feels” mild. Others might be more susceptible to thermal skin damage or otherwise have a pre-existing condition that would rule out saunas of any kind.

Infrared saunas have gained attention from Hollywood A-list fans like Gwyneth Paltrow, Jennifer Aniston, Cindy Crawford and Kim Kardashian among others.

“That’s not why I became interested, of course. I didn’t actually know how popular they were until I started looking into it. I just knew that I really enjoyed the … heat, health benefits or not,” Sullivan said.

But anything that requires no effort yet promises lower blood pressure, lower cholesterol, chronic pain relief and cardiovascular improvement is ripe for suspicion.

“I don’t promote it as doing this or curing that, but I read a lot of scientific papers and reports because I get a lot of questions,” Sullivan said. “I tell them that they said this and they said that, but I don’t have a medical degree so I don’t offer an opinion.”

She confesses to being a lifelong “sun worshipper.” She bathed in the sun and routinely went to tanning salons. She ended that hazardous practice, saying the infrared sauna gives her that old familiar warmth without the damaging ultraviolet rays. Other benefits aside, she said that it soothes her.

Anne Tipton, 55 of Brentwood, Missouri, agrees. “I wouldn’t call it meditation, but I get that kind of sense of well-being,” she said. “I love the sweat. It’s a deep heat from within that just feels great. I feel like I’m sweating out the bad stuff. True or not, that’s how it makes me feel.”