How Saunas Work

Getting Beautiful Skin Image Gallery                                         ©                  It's all about getting a good sweat. See more getting beautiful skin pictures.
Getting Beautiful Skin Image Gallery   © It's all about getting a good sweat. See more getting beautiful skin pictures.

You're going to want to read this article naked, so please, before you go any further, disrobe completely. That's right, socks too. Now grab a towel, claim a spot on your favorite cedar bench and get ready to learn about the pride of Finland and the sweet relief of nude bodies everywhere: the sauna.

If you've never experienced a sauna firsthand, then the photo to the right pretty much sums it up. These hot, dry environments open up your pores, relax your limbs and unleash a cleansing wash of perspiration all over your body. Much like Native American sweat lodges, there's also a mental or even spiritual side to a sauna's soothing qualities.


Thus, saunas appeal to the health-conscious rationalist and the new age dreamer alike -- as well as to the average Finn who just wants to clean off before a swim. According to sauna expert and author Mikkel Aaland, it's customary to have a sauna (in addition to a shower) before entering a swimming pool in Finland.

What separates the sauna from many other steam baths (such as the tiled steam rooms often found in spas) is the type of heat. Steam rooms feature a moist heat, and tend to operate at temperatures of around 104 degrees Fahrenheit (40 degrees Celsius). To heat it up any further, you have to add more steam (a steam room's heat source), which can quickly create a scalding environment. Moist heat also feels hotter because the moisture-rich air prevents your sweat from evaporating and cooling your body.

Saunas, however, use dry heat. With less moisture in the atmosphere, you can safely sweat it out in these hot boxes at temperatures of about 176 degrees Fahrenheit (80 degrees Celsius). Particularly devoted sauna worshipers often brave even hotter conditions.

In the pages ahead, we'll explore the mechanics, culture, history and health benefits of the sauna.


Step Inside the Sauna

Welcome to the inside of a traditional Finnish savusauna, or wood-burning sauna. Note the smoke-blackened walls.
Welcome to the inside of a traditional Finnish savusauna, or wood-burning sauna. Note the smoke-blackened walls.
Ilkka Rinne/Creative Commons License

Now it's time to actually walk inside the sauna and discover how everything works. This is where the whole nudity thing pays off because, as we mentioned, the air inside a sauna is generally around 176 degrees Fahrenheit (80 degrees Celsius). The low humidity keeps conditions bearable, as does all the wood.

That's right, a sauna's handsome cedar or spruce décor isn't merely a stylistic choice. Metal or plastic seats would quickly become downright bun sizzling. Wood, on the other hand, remains relatively cool at high temperatures and proves rather durable. Plus, a wood interior absorbs steam, stores heat and releases soothing aromatics with every use. Tiles sometimes line the room just underneath the wood to help manage moisture and seal in the heat.


As for a sauna's heat source, there are a few different makes to choose from. The oldest form of sauna is the wood-burning sauna or savusauna. Forget the images of fine cedar craftsmanship for a moment and instead envision a chimneyless, windowless wooden shack in the forest. Inside, an open fire heats a pile of rocks as smoke slowly seeps through cracks in the roof. That's a wood-burning sauna. Today, this method is more the domain of sauna purists, as the smoke fills the air with eye irritants and the process of heating up the shack can take all day.

The more typical sauna design retains the basic principle of the savusauna, only without all the smoke. Instead of an open fire, a sauna uses a small stove called a kiuas. The kiuas can be electric, gas or wood burning, but the result is the same: It heats a pile of rocks. In some cases, the stove provides continual heat, while in others it only initially provides heat, which the rocks absorb and continue to emit through the surrounding air.

Not just any variety of rock will do. Sauna rocks have to stand up to high temperatures without cracking or exploding. For this reason, unweathered, quarried rock such as peridotite (a Finnish favorite), basalt and hornblende are often used.

Ready to heat things up? Skip to the next page to find out what that ladle and bucket are for.

Sauna Construction: The Science of Sweat

Note the rock-laden kiuas in this typical Finnish sauna. By ladling water onto the rocks, you can add more humidity to the room and make it feel even hotter. To cool off, you can also ladle the water on your body.
Note the rock-laden kiuas in this typical Finnish sauna. By ladling water onto the rocks, you can add more humidity to the room and make it feel even hotter. To cool off, you can also ladle the water on your body.
© AliquisNJ

There you are in the sauna, heat permeating your body. You inhale and catch a hint of fresh sweat beneath the rich aroma of steamed cedar and maybe a few traditional herbs. Your mind and body drift into a deeply relaxed state, but hold on. What if you want things a little hotter?

Look for that bucket and ladle we mentioned. The kiuas heats the rocks and the rocks heat the air inside the sauna. To raise the temperature any higher, all you have to do is pour a little water from the bucket on the rocks. The water will instantly burst into steam with a sharp cracking sound and maybe a hiss. You've now added humidity to the air in the sauna, elevating the apparent heat. The Finnish term for this hot sauna vapor is löyly.


Sauna construction runs the gamut, from backyard hovels in the woods to just about the ritziest spa faculties imaginable. Maximum occupancy ranges from a single bather to the entire Swiss men's national ice hockey team. In Finland, where saunas are integral to daily life, it's customary to bring portable, folding saunas on camping trips. The soldier's life isn't complete without one either. When the Finnish army sent troops to help restore war-torn Kosovo, the army made sure to construct 20 saunas for its 800-troop contingency [source: Gray]. Even Finnish prisons offer sauna privileges to inmates.

The traditional sauna has remained unchanged for centuries, but if you're itching for something more high-tech, you can always disrobe for an infrared sauna. The aim is still the same: transfer heat to the human body, only instead of depending on hot stones, it directly heats bathers with infrared light. Proponents of this technology argue that infrared provides a superior sauna experience since the infrared radiation penetrates deeper into bone and muscle tissue. They also argue that a session of infrared imparts all the beneficial aspects of sunlight, only without all the blisters and skin cancer.

But let's get back to the traditional sauna and throw a little more water on the kiuas, shall we? What does all this sweating do for your health?

Saunas and Your Sweat

Can you really sweat out all your problems?
Can you really sweat out all your problems?
Katrin Thomas/Photodisc/Getty Images

Steam bathing is a truly ancient custom, dating back to the earliest nomadic tribes. As human culture sprang up like weeds around our physical needs, the notion of personal hygiene merged with those of purity and transformation. Depending on where you're coming from, a little time in the sauna can treat not only soreness or tension, but even spiritual pollution.

Yet amid all the intertwined vines of folklore and placebo effect, a chord of solid medical science supports the notion that, yes, a little time in the sauna is time well-spent. Sweating, no matter how detrimental to a job interview, is a part of healthy living.


This is how it goes down: The heat triggers sensitive nerve endings that release a neurotransmitter called acetylcholine, which kicks 2.3 million sweat glands into action. During the course of a 15-minute sauna, the average person can expect to shed a little more than 4 cups (1 liter) of sweat. Your body does this to control body temperature.

Sweating, like urinating, is a form of excretion and all forms of excretion help to rid the body of waste and/or toxins (though sometimes incidentally). Imaginative creatures that we are, this fact often leads to dodgy and outright false notions that bleeding or experiencing a bowel movement can heal any physical, mental or spiritual ailment.

Likewise, the idea of sweating out your troubles dates back to ancient times, but what does science have to say? In 2005, the U.S. Centers for Disease Control and Prevention (CDC) found that heavy sweat contains only trace amounts of bodily toxins, no matter how high levels are in the blood and urine. Take mercury, for instance: Less than 1 percent leaves the body in the form of sweat, while the rest goes out with the feces and urine [source: Woolston].

Still, sauna detox advocates put stock in this 1 percent and also point to the beneficial secretions of excess salt and uric acid or urea, which is normally handled by the body's big-league detox organs, the kidneys. This method again falls to the "let the kidneys handle it" counterargument, but when kidney function is impaired, sweating it out in a sauna can help to make up the difference.

Ironically, sweating to rid yourself of toxins can actually backfire if you don't remain properly hydrated. The kidneys need water to function, and your water-based urine is the vehicle by which substances such as urea leave your body. Rob your body of too much water and you could wind up impairing your core detox systems [source: Huang et al.].

Saunas and Your Skin

Yes, saunas are such a big deal in Finland that they even make a competition out of it. Here, competitors sweat through the final of a 2003 sauna bathing competition in the town of Heinola.
Yes, saunas are such a big deal in Finland that they even make a competition out of it. Here, competitors sweat through the final of a 2003 sauna bathing competition in the town of Heinola.
AP Photo/Leif Rosas/LEHTIKUVA

Let's forget about toxins for a bit and focus on what else is going on with the human body in the sauna. At the very least, the act of sweating cleans the skin, opens the pores and keeps it pliant.

A 2008 study in the journal Dermatology suggested that regular sauna usage has a protective effect on skin functions and may help with dry skin conditions [source: Kowatsiki et al.]. Of course, it's also important to wipe the sweat from skin following a sauna session, in addition to implementing other skin care practices, such as the exfoliation.


Some sauna cultures also include the use of mild self-flagellation. In Russian saunas called banyas, participants lightly flog their skin with a venik, a small bundle of dried, leafy branches of birch, oak, maple or other plants. This sensation helps to increase blood flow, coats the skin in aromatic plant oils and, like most grooming sensations, stimulates the production of opiate endorphins and dampens nervous system pathways to produce mildly narcotic effects [source: Smith].

In the heat of the sauna, the inner body also carries out another important function. The capillaries dilate, causing increased blood flow to the skin. You may have observed this in the rosy hue of your fellow steam bathers. The heart beats faster to regulate this increased circulation, all without an increase in blood pressure. These conditions create an artificial fever condition in the body. Remember, a fever is the body's response to infection, increasing metabolism, lymphatic drainage and white blood cell count. Outer skin temperature may rise by up to 18 degrees Fahrenheit (10 degrees Celsius), while inner temperatures increase up to 5.4 degrees Fahrenheit (3 degrees Celsius) [source: Aaland].

These changes are not always beneficial, however, especially to individuals with weakened constitutions. For this reason, many doctors advise small children and the elderly to avoid saunas -- especially if followed with a system-shocking leap into a cool swimming pool or a bank of snow (both popular after-sauna exercises). Individuals with heart conditions or high blood pressure are also advised to skip the sauna.

The dry heat of a sauna can also open up clogged respiratory passages, but individuals with pneumonia or other acute respiratory diseases generally are advised to avoid sweat bathing. Likewise, saunas can greatly alleviate menstrual cramps and various soft tissue, muscle and joint pains, but the increased heat can introduce increased risks for pregnant women.

The Saga of the Sauna

Created in 1496, Albrecht Dürer's "The Women's Bathhouse" realistically depicts the German public bath culture of the day.
Created in 1496, Albrecht Dürer's "The Women's Bathhouse" realistically depicts the German public bath culture of the day.
Mario Tama/Getty Images News/Getty Images

In discussing saunas, it's important to note the antique origins of the Finnish practice and of saunas themselves. The practice spans the breadth of human history, back to when Neolithic tribes inevitably happened across geothermic hot springs and steamy caverns.

Just imagine the sensation of walking in from the cold of a Stone Age winter and finding yourself in a hidden pocket of summer. Imagine stripping off your hides and feeling months of accumulated dirt wash off you in a tide of dripping sweat. It's the sort of thing you can get used to, right? And that's just what our early forefathers did. The ancient cave settlements in France and Spain are handily situated within walking distance of hot springs. Since then saunas have found their way into cultures throughout the world, from the African motherland to the wilds of precolonial America.


The Finnish have sat in saunas for as long as they've been a people. It's thought that they brought the practice with them when they migrated into modern Finland, splintering off from other nomadic Asian tribes. Like many northern peoples, including Native American tribes, they likely used portable sweat lodges until a more settled lifestyle allowed them to construct semipermanent structures -- dugout smoke lodges, then the first savusaunas and finally saunas.

Up through the Middle Ages, bathhouse culture ran rampant through Europe. Whole villages of common men, women and children would sluice it up at the local bath house. They'd feast amid the steaming vats, as well as hold birthing and marital ceremonies. They'd also partake of the kind of carnal indulgences that earned them such nicknames as "the stews." They were kind of a catchall venue for every aspect of common life, a place for weekly cleansings in both the hygienic and ceremonial senses -- and of course, a great place to meet prostitutes.

Then, in 1517, the Protestant Reformation came, along with syphilis, plague and rising fuel costs. Together, these forces all but washed public baths from Europe. Only the Finnish, Scandinavians and Russians held tight to their traditions.

We've covered a lot of ground, but now it's time to answer the final pressing question: How naked should you be in the sauna? Don't put a stitch back on -- just click to the next page.

Saunas Nudity and Etiquette

This couple opted to sauna toweled. However, it's worth noting that we have no idea how naked the photographer is.
This couple opted to sauna toweled. However, it's worth noting that we have no idea how naked the photographer is.
Holde Schneider/Bongarts/Getty Images

If you've been following instructions, then you've read the previous six pages completely naked. If you're actually Finnish, there's a good chance you went the extra mile and read them on your iPhone whilst ladling water on the kiuas. But all this leads to the inevitable question: How naked do you need to be in the sauna?

Obviously, for a comfortable, effective sauna experience, you'll need to be as naked as possible. From there, everything breaks down into whatever the accepted local sauna culture happens to be. In Finland, for instance, you'll find both mixed-sex and single-sex nude saunas. But don't fret, bashful foreigners. No one is going to overreact if the shy American wishes to wear a towel. Hey, it's your loss for missing out on the sauna experience in its purest form, right? If you do go nude, however, all saunas will require you to sit on a towel.


Outside of Finland, gender divisions and nudity vary greatly. Germany, Austria, Scandinavia and Eastern Europe generally offer nude, mixed-company bathing. Russian banyas and South Korean jjimjilbangs are both traditionally gender-separated, but usually quite nude as well. Covering up with a towel is fine, but many establishments will frown on the wearing of shorts or even swimwear for hygienic reasons.

Other countries, such as France, Italy, Spain and the United Kingdom tend to offer same-sex facilities and are perfectly fine with nudity. Walk into a London sauna and you're likely to encounter a mixture of sauna cultures: stark-naked Scandinavians, towel-clad Brits and Americans snugly packed in their Speedos. Across the pond, however, you'll find a different scene. If you're planning to break a sweat in a U.S. sauna, then you're probably going to have to cover up.

Beyond the issue of nudity, also keep in mind that many cultures frown on talking in the sauna or bringing in outside items such as newspapers or a phone. Certainly, never try to smuggle a sandwich in with you. There's often additional etiquette surrounding when to pour water on the rocks, as well as when to enter or exit the sauna. In German-speaking countries, only the official saunameister may pour water on the rocks, and patrons are expected to enter and leave the sauna in strict 10-minute intervals. By all means, do not tempt the wrath of your saunameister.

Finally, it's always a good idea to pay attention to posted rules and follow the example set by sauna regulars. And whether you're sitting in your shorts at a Baltimore YMCA or experiencing a traditional savusauna nude in the taiga forests of northern Finland, remember to relax. Let the heat do its work and lose yourself in a cleansing rite as old as civilization itself.

Explore the links on the next page to learn even more about saunas and skin care.

Lots More Information

Related HowStuffWorks Articles

  • Aaland, Mikkel. "Sweat." Cyber-Bohemia. 1997. (Sept. 1, 2009)
  • Buford, Darren. "No Sweat!" Body Sense. August 2005. (Sept. 1, 2009)
  • "Finland takes gold in World Sauna Championships." Telegraph. Aug. 9, 2009. (Sept. 3, 2009)
  • Gray, Andrew. "For a Finnish Soldier, Home Is His Sauna." ABC News. Aug. 31, 2009. (Sept. 3, 2009)
  • Huang, C.T. et al. "Uric acid and urea in human sweat." National Yang-Ming University Institute of Public Health. Sept. 30, 2002. (Sept. 2, 2009)
  • Kowatzki, D. et al. "Effect of Regular Sauna on Epidermal Barrier Function and Stratum Corneum Water-Holding Capacity in vivo in Humans: A Controlled Study." Dermatology. June 5, 2008. (Sept. 3, 2009)
  • "Sauna Etiquette -- Eliminate Potential Surprises." 2009. (Sept. 4, 2009)
  • Smith, Virginia. "Clean: a history of personal hygiene and purity." Oxford University Press. 2007.
  • Stix, Gary. "Heavy-Metal Sweat." Scientific American. October 2005. (Sept. 3, 2009)
  • "Sweat It Out." Men's Fitness. June 2009. (Sept. 3, 2009)
  • Toothman, Jessika. "How Hyperhidrosis Works." April 28, 2008. (Sept. 3, 2009)
  • Vandervort, Dan. "Sauna wood." Dan Vandervort's Home Tips. (Sept. 3, 2009)
  • Williams, Jack. "Latent heat supplies weather energy." USA Today. 2008. (Sept. 8, 2009)
  • Woolston, Chris. “The Healthy Skeptic.” Los Angeles Times. Jan. 28, 2008. (Sept. 9, 2009)