We all know that breaking a sweat is beneficial: It means we’re exerting ourselves, our blood is pumping, oxygen is flowing into our lungs and energizing our cells. But there’s an added bonus—it’s also a major beauty boost. “We tend to think about the benefits of exercise in terms of fitness, and we even recognize its ability to lift our mood and help with sleep, but we don’t usually think of its profound role in keeping skin looking young and firm,” says Manhattan dermatologist Whitney Bowe, MD. This isn’t just because physical activity boosts the metabolism of cellular mitochondria and prevents the thinning of skin that occurs with age, it’s also because the schvitz itself acts to purify, protect, and rejuvenate the complexion.

Perspiration, that salty brew of H2O and minerals many consider to be one of the body’s less savory secretions, is essentially the body’s air-conditioning system. Its evaporation on the surface of the skin keeps us from over-heating, and regulates our core temperature when things get toasty—either internally or externally. “It helps with water balance for your entire body,” says dermatologist Doris Day, MD. “It also contains natural moisturizing factor, which helps keep the skin hydrated and healthy.” Even though most of us rush to wash it off post workout (and rightly so, since its urea content can irritate the epidermis if left long un-rinsed), it’s actually bolstering the microbiome while it sits on skin. Sweat is the source of an antimicrobial peptide called dermcidin, says Bowe, “which helps protect against infection from harmful germs, like a natural antibiotic.”

Humanity’s love of sweating it out (whatever it is) in saunas, steam rooms, and bikram yoga, is as old as time, and as universal as sweat glands themselves, from Native American sweat lodges to Scandinavian saunas to Turkish hammams. Even the ancient Romans had “caldarium” rooms in their great bath houses, where they would bask sans togas in furnace-heated steam. It’s never been simply about staving off a chill; and while the cardiovascular benefits are real, what’s most strikingly evident post-sweat-sesh is an invigorated appearance. “When our body temperature rises, our blood vessels dilate,” says Bowe. “This is called vasodilation and it increases the flow of blood to our skin. Over the long term, vasodilation has a positive impact on the vasculature that supports our skin, helping to keep our skin looking healthy and youthful.”

The hottest new arrival on the sweat scene, both metaphorically and literally, is the infrared sauna, in which the body is warmed from the inside out to a sweltering 120 degrees by infrared light waves. “Because the heat from an infrared sauna is so much deeper and more intense in the body’s core, that helps you sweat more profusely,” says Sasha Sabapathy, the founder of London’s Glow Bar, a chic infrared spa and adaptogen-tonic café near Oxford Circus. “It’s amazing because it really helps clear out your pores. In cities like London, New York, and Los Angeles, it’s almost impossible to clear all the pollution off of your skin, and a lot of people aren’t cleansing properly and getting everything off, so sweating helps to give your skin a good purge.” And it’s not just de-gunking: “People often comment, too, that their dead skin cells come off a lot faster with the sweat,” says Sabapathy. “It leads to an overall full-body glow, because you’re getting rid of that dull, dead layer.”

If you’re in it for the skin benefits, is there an optimum way to perspire? Day says that when it comes to sauna versus steam versus SoulCycle, “sweat is sweat, but workouts are healthier for you overall.” Bowe concurs: “In my opinion, sweating through exercise is the way to reap the full range of benefits. Saunas and steam rooms are more like short cuts. Yes, you get vasodilation, which improves circulation, and yes, you get that release of antimicrobial peptides, but you are not likely to affect the mitochondria in any meaningful way.” However, she admits, there’s a caveat: The stress-reducing benefits of a good sauna or steam “might positively impact the gut-brain-skin connection, ultimately benefiting skin.”

Sabapathy has seen positive changes in her own complexion, and improvements in her clients’ acne—and believes it’s the chill-out-factor, just as much as the sweat, that’s making the difference. “The heat gets your blood pumping faster, which creates an oxygen surge that boosts serotonin in the brain,” she says. “Most people’s breakouts are caused by high levels of cortisol, which also contributes to anxiety and depression, so an increase in serotonin can balance that out. You’re getting a calmer mind, and you’re getting clearer skin. It’s a win-win.”

FWIW, Kate Hudson is all about the benefits of the infrared sauna and if you’re interested, here’s what it’s really like to sit in one for 30 minutes.