The science of sweating

Many cultures have ritualistic perspiration ceremonies, if not currently, at least at some point in their history. Marbled hammams dot the Middle East; Native Americans have sweat lodges; Koreans attend jjimjilbangs; The Russians drink vodka in banyas; and the Finns exported saunas across the western world. For many people, there is something both calming and cathartic about sweating in large quantities.

The fascinating work of the towels is at the heart of the Aufguss ceremony, as it distributes thick gusts of hot wind around the sauna. Like the opposite of a winter wind chill, which makes you feel colder, the steam wind makes the sauna warmer. A good Aufguss master can produce enough wind during the ten minute ceremony that your hair will blow in the breeze, even though sweat is flooding your skin.

Shedding isn’t just sweat: Scientists have found that in a wet sauna, between 30% and 55% of the fluid rolling over your body is actually condensed water. The skin temperature in a sauna rises a few degrees above normal (up to around 109 ° F), but the rest of the space is typically around 175 ° F to 195 ° F, and the vapor is above 210 ° F. Because your body is one of the coolest objects in the room, evaporated water there condenses like steam from a kettle on a cold winter window.

At the end of an Aufguss ceremony, it is not uncommon to float on a wave of euphoria that is the product of both brain biochemistry and basic physiology. When your skin temperature rises in a sauna, so does your pulse. After 10 to 15 minutes indoors, your heart may beat about 120 to 150 beats per second. For many people, this is the equivalent of light exercise. Sauna sessions increase blood levels of epinephrine, growth hormone and endorphins, the latter also being hormones often held responsible for a runner’s euphoria. With a sauna you get bliss without mileage.

Trying to capitalize on humanity’s love for a good sweat, spa entrepreneurs often promise clients a cornucopia of health benefits, many of which border on pseudoscience and even rubbish. Going to the sauna is not a smart chemical detox strategy; in fact, sweating is not a detoxification strategy at all, and calling it one reveals a fundamental misconception about how the human body works.

Sweat comes from the liquid parts of the blood, minus the large elements like red blood cells, platelets and immune cells. All the chemicals floating around in the circulatory system can emerge in sweat, good substances like glucose and hormones and unwanted substances like heavy metals and urea. But if you are actually detoxing yourself through sweating, you will need to expel all the fluid in your blood to get rid of the nasty stuff. It would leave you completely dehydrated and possibly dead. Instead, your kidneys filter problematic chemicals from your blood and send them out in the urine.

Sweat is only responsible for cooling us down; everything that comes out of it is fortuitous, just for the path of the blood plasma to the surface of our skin. That’s why humans need to replenish our precious bodily fluids after an epic sweat, a problem studied by Michael Zech of the Dresden University of Technology.

Sitting in a sauna, watching the sweat drain from his body, Dr. Zech wondered how long it would take for a sip of water to pass from his lips to his pores. Before his next sweat, he slipped a chemical tracer into his favorite sauna rehydration drink. He drank a little over a pint, undressed, and entered the sauna. At regular intervals, he captured his sweat droplets in small glass vials.

In his lab, Dr Zech checked the samples and found that it took less than 15 minutes for the tracer to pass through his stomach, either absorbed through the intestine, or filtered through the liver and kidneys, into his stomach. blood flow, passes through his circulatory system. system to reach the veins in her skin, diffuse through her dermis to the sweat glands, and then escape millions of pores in her skin. His question answered, Dr Zech went back to sweating for fun instead of science.

Serious scientists haven’t neglected the sauna, but many questionable health claims about it come from questionable research conducted decades ago. For example, there is an oft-repeated claim that going to the sauna strengthens your immune system and helps prevent colds in winter. Evidence for this comes from a handful of studies from the 1970s and 1980s that even one promoter called “mostly retrospective and poorly controlled.”

However, the sauna has been shown to be great for your heart. This finding is based on a large study of Finnish men since the mid-1980s. Men who used sauna regularly had a lower incidence of sudden cardiac death, fatal coronary artery disease, fatal cardiovascular disease, and mortality, which means, in short, that going to the sauna regularly could help prolong life.

Of course, for Finnish men, “going to the sauna regularly” means more than four times a week. Given the widespread cultural habit of sweating regularly among Finns, scientists used men who went to the sauna once a week as a baseline and compared their health to that of men who went more often.

However, the finding is striking. Even if you normally relax in the sauna, your circulatory system is not. He is at full blast, trying to take the warm blood from your interior and bring it through the veins near the surface of your skin, where the evaporation of sweat cools the passing blood. All that blood pumped through the circulatory system gives your heart a workout and provides training biochemical effects that likely activate plaque removal and other benefits to your circulatory system.

But don’t cancel your gym membership yet. Sitting in a sauna doesn’t burn as many calories as a workout, and you neither build nor strengthen your muscles. Still, for people who can’t exercise, going to the sauna can be a good first step towards heart health. Attending an Aufguss ceremony can also give it an artistic touch.

–Ms. Everts teaches journalism at Carleton University in Ottawa, Canada. This essay is adapted from her new book, “The Joy of Sweat: The Strange Science of Transpiration”, published by WW Norton.