Everything You Always Wanted to Know About Sweat

If you added up Christopher Bergland’s athletic achievements, they would amount to the equivalent of running around the world four times, biking to the moon and back, and swimming across the Atlantic Ocean and home again.

The tenacious endurance athlete once set a Guinness World Record for running — 153.76 miles on a treadmill in a single day — and is a three-time Triple Ironman champion, completing the überdemanding 7.2-mile swim, 336-mile bike ride, and 78.6-mile run in a record-breaking time of 38 hours and 46 minutes his first year.

Bergland knows a thing or two about sweat.

“When I finished the Triple Ironman, I felt like I’d sweated out every last electrolyte,” he says. Fortunately, Bergland, author of The Athlete’s Way: Sweat and the Biology of Bliss, takes inspiration from perspiration.

“I love to sweat,” he says. “In my mind, sweat equals bliss.”

Sweat is a common partner to exercise, whether it’s the rivulets that accompany an intense weightlifting circuit or the droplets that pitter-patter onto our yoga mats during downward dog.

But outside of working out, we rarely celebrate perspiration as a desirable byproduct. In fact, if we think of sweat at all, many of us consider it an embarrassing bodily function, a sometimes-stinky annoyance, a socially undesirable bit of physiology.

On an exciting first date, for instance, your palms may get sweaty just as that special someone reaches for your hand. At a job interview, underarms can turn swampy after the first tough question.

Even in the context of a great workout, sweating buckets can be less than comfortable. “Breaking a sweat can create some inconvenience,” acknowledges Bergland, “but the payback is always going to be worth it.”

If it weren’t for sweat cooling our bodies down, we’d all perish much sooner.

Why?

Because sweat serves a purpose — as a barometer of effort, as an indicator of stress, as a measure of health, and also as a literal lifesaver: If it weren’t for sweat cooling our bodies down, we’d all perish much sooner.

Perspiration is a nearly universal experience. But how many of us really understand how it works, and why? Here are the fascinating essentials you need to know — the cut-and-dried facts about all things sweaty.

Why do we sweat?

Like it or not, we can’t live without sweat.

Perspiration keeps the body from overheating and short-circuiting. When your core temperature rises much higher than 98.6 degrees F, the hypothalamus — your brain’s thermostat — signals the exocrine system’s sweat glands to activate. Perspiration rises to the skin’s surface through pores and evaporates when it hits the air, keeping you cool.

We often sweat during exercise, but plenty of other conditions can prompt sweating, like a hot summer day or situations that make us feel anxious, embarrassed, or angry.

What is sweat, anyway?

You’ve no doubt noticed that sweat can taste salty. Perspiration is mostly water, along with small amounts of fat and electrolytes — the electrically charged essential minerals (such as sodium, potassium, and calcium) that are critical to our body’s function, including muscle contractions and energy production.

Sweat’s makeup differs depending on which kind of sweat gland — eccrine or apocrine — produces it.

Eccrine glands are found all over the body but are most concentrated on the forehead, palms of the hands, and soles of the feet. These glands produce a clear, watery fluid when you exercise or are too toasty.

Don’t blame eccrine sweat for body odor, though; this type of perspiration doesn’t smell. If your feet are stinky, it may be due to an overgrowth of the Micrococcus sedentarius bacteria, which grow when feet are enclosed in socks and shoes all day.

Apocrine glands, on the other hand, produce a milky fluid that is responsible for BO. They are found primarily in areas abundant in hair follicles — such as the underarms and genital area — and expel a thick, oily fluid containing fats and proteins.

Apocrine sweat doesn’t innately smell bad, but when it interacts with the millions of bacterial organisms (such as Staphylococci or Corynebacteria) that live on the skin’s surface, it produces a telltale odor.

How much do we sweat?

More than you might think: According to the National Institutes of Health, an average adult can produce up to a quart of sweat per day. Children don’t start reaching those levels until puberty.

How many sweat glands do we have?

We are born with between 2 million and 4 million sweat glands, which are located all over our bodies — except a few places, like our lips and ear canals.

Why does my sweat stink when I’m stressed?

Remember the Saturday Night Live schoolgirl character, Mary Katherine Gallagher, who would stick her fingers under her arms and then smell them whenever she got nervous? It’s likely she was getting a whiff of something strong. Sweat produced when we’re under emotional stress is made by the apocrine glands, which are responsible for the stinky sweat.

What exactly triggers stress sweat is still unclear, though scientists hypothesize that it’s linked to the adrenaline release that accompanies a fight-or-flight situation. This serves as an evolutionary — and odorous — warning signal.

Stress may also cause a vicious circle of sweat: When you notice you’re perspiring a lot, it can increase your anxiety — What if someone notices my wet underarms?  And this in turn can make you sweat even more.

Why do some people sweat more than others?

Thank your parents for this one.

A big factor in how much you sweat is genetics, which determines exactly how many sweat glands you have. It’s also affected by other factors, including sex (see “Sweating and the Sexes” further down), fitness level, health status, and weight.

Heavier people tend to have higher sweat rates, both because they have to exert a lot of energy during physical activity and because there is more body mass to cool down. Surprisingly, though, the sweatiest people in the gym are often the fittest.

Surprisingly, though, the sweatiest people in the gym are often the fittest.

“People who are highly fit generally maintain a higher sweating rate, due to more muscle mass (which is heat-producing) and having a greater blood volume and circulatory system, along with a greater sweat-gland capacity and sensitivity,” says Michael Bergeron, PhD, a fellow of the American College of Sports Medicine. “And, of course, the more fit you are, the longer and harder you can exercise, and thus, the more you will sweat overall.”

Does sweating change with age?

There’s a reason babies and little kids smell sweet: Their apocrine glands aren’t yet active. Once puberty hits, and the apocrine glands start functioning fully, body odor can become an issue.

Another shift happens in midlife. About 75 percent of women experience hot flashes and sheet-soaking night sweats during perimenopause and menopause. This excessive sweating is probably caused by changes in reproductive hormones and changes in the body’s thermostat, says Rebecca Thurston, PhD, director of the Women’s Biobehavioral Health Laboratory at the University of Pittsburgh. “The central thermostat of the body malfunctions during menopausal transition,” she says.

Women can experience hot flashes or night sweats for several years. “We used to think the duration that a woman will have hot flashes and night sweats was three to five years,” says Thurston. “But the newest data shows that the really frequent, severe ones maybe last seven or eight years; and low-level symptomatology is probably closer to 10 years.”

Some doctors prescribe hormone therapy to ease the discomfort of night sweats, but many are working to develop nondrug approaches. Studies have shown that not smoking, maintaining a healthy weight, and using herbs like black cohosh may help. And Thurston notes that “the most effective behavioral treatment right now is hypnosis — believe it or not — with cooling suggestions.”

(For more on night sweats, see “What Causes Night Sweats?“.)

What does the scent of sweat tell us?

Sweat may play a role in nonverbal human communication. The “sweaty T-shirt study,” for example, conducted by Swiss biologist Claus Wedekind in 1995, found that women rated most pleasant the scent of men whose genes were most unlike their own, suggesting attraction to a potential mate who’d ensure a stronger immune system for their offspring. Talk about chemistry!

Sweat can also speak poorly of us. Research published in PLOS ONE in 2013 shows that ­women’s stress sweat can make men perceive them as less confident, competent, and trustworthy.

And a report published in Psychological Science found that we can detect other people’s emotions, thanks to sweat. In fact, researchers from Utrecht University in the Netherlands suspect that sweat’s scent actually makes emotions contagious.

In the study, underarm sweat was collected from men as they watched scary scenes from The Shining and gross-out clips from the TV show Jackass. When women smelled the “fear sweat” samples, they opened their eyes wide and had a frightened expression. When they smelled the “disgust sweat,” they grimaced.

Why do some people sweat excessively?

About 3 percent of the world’s population has hyperhidrosis, which causes someone to sweat a lot — four to five times as much as the average person.

“Primary hyperhidrosis, while not life threatening, is certainly life altering,” says Lisa Pieretti, executive director and cofounder of the International Hyperhidrosis Society. “The extreme embarrassment as well as actual functional impairment can be devastating. But thankfully, we see great improvement in the treatments being offered and the awareness of both the public and medical communities.”

While primary hyperhidrosis appears to have a genetic component, secondary hyperhidrosis can result from an underlying condition, such as lymphoma, hyperthyroidism, or diabetes, or as a side effect of medication. Treatments include Botox injections, iontophoresis (which sends a gentle electrical current through your body to shut down sweat glands temporarily), and even surgery.

Still, some doctors suggest that hyperhidrosis can be vastly improved by testing for food-sensitivities and removing any offending foods from the diet.

Should I be concerned if my sweat suddenly smells different?

It’s normal for foods like garlic to temporarily alter our body odor as their chemical compounds are excreted through our pores. Yet strong BO can, infrequently, signal a health issue.

Trimethylaminuria is a rare genetic disorder that causes sweat to smell like rotting fish or eggs. Research has also linked certain body odors to kidney failure, schizophrenia, and olfactory reference syndrome, a delusional condition in which patients believe they have a bad body odor but in reality do not. These conditions are rare but should be addressed by a medical professional.

Why do certain clothes smell worse than others after we sweat?

A study published in the journal ­Applied and Environmental Microbiology shows that polyester apparel retains stink more than ­cotton clothing after a hard workout, because it is less absorbent and promotes odor-causing bacteria.

“We investigated the microbial growth on both textile types, and it appeared that different microbial growth occurred,” says Ghent University’s Chris Callewaert, PhD, senior postdoctoral research fellow at Research Foundation Flanders and creator of the website DrArmpit.com.

“Polyester was a source for Micrococcus enrichment, which was not seen on cotton. Micrococci are known for their enzymatic capacity to degrade fatty acids and amino acids into volatile malodorous compounds. These microbes are also an important reason why polyester is stinkier after exercise.”

Like natural cotton, wool can help you avoid a smelly clothes hamper. While wool will permit microbial growth, it breeds mostly nonodorous bacteria.

Workout wear is often made from synthetics like Lycra and polyester, which can wick away sweat but hold on to body odor. Specially formulated detergents can help dissolve the oils that ­interact with bacteria and cause the smell. Antimicrobial sportswear can also help reduce the microbial numbers, but it comes with its own risks. (For more on why ­anti-odor clothes stink, see “Why Anti-Odor Clothes Stink“.)

These measures prevent the sweat that’s absorbed into the treated material from becoming stinky. But be forewarned that bacteria on your skin can still transform the sweat molecules into something malodorous.

(For smart advice on getting funky odors out of gym clothes, see “How to De-Stink Your Sweats“.)

Is it possible to sweat too little?

Yes. Sweating too little — a condition called anhidrosis — can be life-threatening, because the lack of sweat can lead to heat exhaustion or heat stroke.

Anhidrosis occurs when your sweat glands stop working. It may be caused by nerve damage, burns, certain medications, genetics, or dehydration.

If anhidrosis affects only a small area of your body, it’s typically not harmful. If you can’t sweat from a large area of your body, however, it’s wise to seek medical counsel.

Do certain foods make us sweat?

Just like hot weather, hot-tasting foods raise your body temperature, affecting the receptors in your skin that tell the nervous system to kick into cool-down mode and produce sweat.

In addition to five-alarm chili and kicky curries, substances like caffeine, nicotine, and certain prescription drugs can also stimulate the sweat glands. And drinking large amounts of alcohol promotes profuse sweating, too, by increasing your heart rate and dilating the blood vessels in your skin.

Extreme food-related perspiration is called gustatory sweating, or Frey’s syndrome. While it is sometimes linked to conditions like diabetes and Parkinson’s disease, many cases happen after trauma to a parotid gland — the largest salivary glands. When damage occurs, individuals may sweat when they are supposed to salivate.

What are the health benefits of sweating?

Aside from its temperature-regulating effect, sweating has been shown in recent studies to excrete small amounts of toxins, including arsenic, mercury, lead, and cadmium, as well as to rev up circulation and clear the pores.

Researchers have found that exercise is not the only way to reap these rewards — saunas can be a part of your sweat-inducing regimen. Infrared saunas, in particular, which heat the body without warming the surrounding air, can provide such benefits as improved circulation and pain relief. Scientists are exploring the use of this therapy in treating health issues like rheumatoid arthritis and high blood pressure.

Still, many experts contend that perspiration’s key benefit is its ability to prevent overheating — not ridding our bodies of unwanted pollution — noting that sweat’s detoxification powers are mild compared with that of our kidneys and liver.

Does sweating protect me from overheating?

Not necessarily.

For sweat to cool us down, it needs to evaporate into the air, and humidity makes that difficult. For this reason, experts warn against overdoing it at hot-yoga studios; when exercising outdoors on a hot, humid day with little to no wind; and when sitting in a steam room. The sweating itself isn’t dangerous, but humid environments can make it ineffective.

“You will still sweat — a lot!” says Bergeron. “But sweat beading up on your skin and rolling off onto the ground is not helping you to regulate temperature.”

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The Science of Stink

Several factors, in addition to your emotional state, can influence your body odor:

• People of East Asian descent are less likely to have BO than their European and African counterparts, thanks to ABCC11 gene variations thought to play a role in the excretory function of apocrine sweat glands.
• A study from Charles University in the Czech Republic found that heavy meat-eating can make your sweat smell worse. Researchers collected the underarm sweat of men on meat-eating or vegetarian diets. Sniffers rated the non-meat-eaters’ sweat significantly more pleasant.
• Some people are cursed with especially stinky feet, thanks to an overgrowth of the bacteria Micrococcus sedentarius, which emit a sulfuric smell.
• Damp skin can encourage bacterial and fungal over­growth, which interacts with apocrine sweat to produce odor, so be sure to thoroughly dry off after a shower or bath.
• The sweat of identical twins smells the same, according to a study published in the Journal of the Royal Society Interface, even when they don’t eat the same foods.
• If you have yellow, sticky ear wax, you’re more likely to have strong body odor. If you have white, flaky ear wax, you’re less likely to smell, according to a 2009 BMC Genetics study.

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The Lowdown on Deodorants

We often turn to deodorants and antiperspirants to smell fresh. There’s a difference between the two:

• Deodorants mask scent.
• Antiperspirants obstruct the sweat glands, stopping odor before it starts.

Although these products can be effective, there’s a chance they will make you stinkier. “Deodorants and antiperspirants have a big effect on the composition and diversity of our armpit microbiome,” says Ghent University researcher Chris Callewaert, PhD.

When deodorants or antiperspirants are used consistently, the armpit microbiome is stable, but when use is stopped or resumed, the axillary microbiome can change, leading to more odor-causing Corynebacteria.

Antiperspirants may also be detrimental to your health. Though the research is inconclusive, they have been linked to breast cancer and Parkinson’s disease, and both antiperspirants and deodorants can contain nasty chemicals like parabens and hormone-disrupting fragrances.

Antiperspirants may also be to blame for yellow underarm stains, which are thought to be caused by the interaction of sweat with the aluminum used in antiperspirants.

Instead of commercial antiperspirants or deodorants, choose clothing made from cotton and other natural textiles, and try out a homemade deodorant made from cornstarch, baking soda, and coconut oil, a natural antimicrobial. (Make your own deodorant with this quick and easy recipe.)

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Sweating and the Sexes

There are distinctions in how males and females perspire. “Males and females have a different armpit microbiome,” says researcher Chris Callewaert, PhD. ­Females’ armpits tend to harbor more Staphylococci, while males’ have more Corynebacteria, which tend to cause more malodors. Transgender individuals may experience differences in odor and amount of sweat, depending on hormone levels.

Females:

Males:

Females don’t sweat as readily as males do, requiring a higher body temperature for their sweat glands to start working, notes a study published in Experimental Physiology. Menstrual cycles can affect sweat; during ovulation, body temperature rises, increasing sweat levels, and menopause can cause profuse sweating. Females have greater sweat-gland density than males, but females sweat less. Females are more able to sniff out body odor, according to research published in the Flavour and Fragrance Journal.

Males have more apocrine sweat glands, which are responsible for BO, than females do. Some studies say males typically sweat more than females — by one report, they produce up to four times more sweat — while others find that sex is statistically less relevant than body morphology, weight, and fitness level. Male BO is harder to hide. One report says that 25 different fragrances were able to mask the smell of female sweat, while only nine worked on male sweat.