13 Surprising Facts About the Armpit

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The human body is an amazing thing. For each one of us, it's the most intimate object we know. And yet most of us don't know enough about it: its features, functions, quirks, and mysteries. Our series The Body explores human anatomy, part by part. Think of it as a mini digital encyclopedia with a dose of wow.

Tucked away in that damp crevice between your arm and torso, the armpit—a.k.a. the axilla—is often the source of unpleasant odors and embarrassing wetness, and a hairy font of annoyance. But it's also an important juncture that protects important lymph nodes and soft tissue. Mental Floss spoke to microbiologist Alex Berezow, a senior fellow of biomedical science with the American Council on Science and Health, about this often overlooked spot. Here are 13 things we learned.

1. YOUR ARMPITS ARE CHOCK FULL OF LYMPH NODES.

In the small hollow of each armpit are a surprisingly large number of lymph nodes, approximately 20, in two clumps, though you can't usually feel them unless they're swollen. (One clump is closer to the surface than the other.) These lymph nodes are actually an important part of your body's immune system and serve to filter toxins out of tissues. They also produce a variety of immune cells known as lymphocytes that fight infection. In some kinds of breast cancer, these affected lymph nodes may have to be surgically removed.

2. THEY PRODUCE A DIFFERENT KIND OF SWEAT FROM OTHER BODY PARTS.

Not all sweat is created equal. In fact, your skin has two types of sweat glands that help to cool you down: eccrine glands and apocrine glands. Eccrine glands cover most of the surface of your body, and are responsible for that thin sheen of sweat on your brow and extremities during heat and exercise. However, your armpits are abundant in apocrine glands (also found in your groin). These glands are copious in places with more hair follicles, and the sweat they secrete tends to be thicker.

3. YOUR PITS ARE TEEMING WITH BACTERIA.

Your skin is home to many different kinds of bacteria, some of which are quite beneficial, collectively known as a microbiome. This microbiome can vary depending on the body part—so the bacteria on your hand can be vastly different from the moist, warm, dank environment of your armpits.

"Because of oil and sweat secretion, the armpit provides a nice home for many different kinds of bacteria," Berezow tells Mental Floss. Compared to other parts of our skin, armpits are rather densely populated, he explains. Not only that, but armpit microbiomes vary from person to person. "One study showed, after sampling nine people, that there were three types of armpit bacterial communities: One was dominated by Betaproteobacteria, a second by Corynebacterium, and a third by Staphylococcus. So one person's armpit bacteria won't necessarily be the same as somebody else's."

4. IT'S NOT YOUR SWEAT THAT STINKS.

"The secretions our armpits make don't stink. Bacteria break down the compounds, and those breakdown products stink," says Berezow. The bacteria that live in the moist crevices of your armpits interact with your sweat, which contains volatile fatty acids and odorous steroids (among other compounds). That creates a product known as thioalcohols, whose oniony, meaty scents you're likely familiar with if you've ever been stuck in a crowded elevator, subway, or gym at peak workout time.

5. SCIENTISTS ARE WORKING ON A DEODORANT THAT WOULD KILL ONLY SOME BACTERIA…

The researchers plan to engineer a deodorant that would kill only the stink-producing bacteria, instead of the entire armpit microbiome. That's because some good bacteria also live under there, like those that help protect you against fungal infections.

6. …BECAUSE REGULAR DEODORANTS CHANGE YOUR ARMPIT MICROBIOME.

…and not necessarily for the better. "Deodorants change the composition of the microbiome," Berezow says. He cites a study that found "antiperspirant reduces the number of bacteria in our armpits, but interestingly seems to encourage a greater diversity of microbes." He adds, "deodorant seems to increase the number of bacteria compared to people who don't wear deodorant."

Scientists have also found that the pits of people who usually use antiperspirants or deodorants, but stopped for a couple of days as part of the study, grew crowded with an overabundance of Staphylococcaceae—the bacteria that causes staph infections. The individuals who habitually did not use products were dominated by the friendlier—and yet stinkier—Corynebacterium. We just can't win. 

7. WHY DON'T YOUNG KIDS' PITS STINK?

While teenagers often exist in a funk so tangible you can almost see it, most children do not begin to have stinky pits until their tweens. A process called adrenarche begins around age eight for some kids (but often even later) in which the adrenal glands start to secrete hormones called androgens. While these are typically thought of as male hormones, both boys and girls produce them in different quantities. At this stage, not only can sweat start to take on its pungent stench, but children can begin to grow armpit and groin hair. Not much is understood about adrenarche, except that it may be a necessary step in order to trigger puberty. Which may explain why middle school locker rooms do tend to get whiffy.

8. WOMEN'S PITS SMELL LIKE ONIONS AND MEN'S LIKE CHEESE.

Researchers from Firmenich, a company in Geneva, set out to understand the subtle nuances in body odor to better market deodorant products to consumers. In their 2009 study, published in Chemical Senses, they discovered that your unique bouquet may be different depending on whether you're a cisgender man or woman. Women's sweat contained higher levels of an odorless sulphur-containing compound that produces a pungent oniony thioalcohol when combined with the bacteria in the underarm. Men's sweat held higher levels of a fatty acid that produced a "cheesy" scent when the bacteria of the armpit came in contact with it.

9. WOMEN DIDN'T ALWAYS SHAVE THEIR ARMPITS.

Since women were socialized to keep most of their bodies covered for centuries, exposing an armpit was an unlikely event in a public place before 1915. However, an ad in Harper's Bazaar changed everything when it suggested that in order to engage in "Modern Dancing," women should first remove their "objectionable" underarm hair. By the Roaring Twenties, many women's pits were as hairless as the day they were born.

10. SOCIAL EXPECTATIONS SHAPE OUR COMFORT WITH ARMPIT HAIR.

Despite armpit hair being as natural as the hair on our heads—and everywhere else it grows—women's armpit hair tends to be controversial. A feminist scholar set out to explore some of the reasons for this in a 2013 study in the Psychology of Women Quarterly and found that social expectations play a huge role in women seeing body hair—on themselves and on other women—as "disgusting" or simply socially unacceptable. Even women who purposely grew their pit-hair out to flout societal expectations felt self-conscious showing armpit hair in social settings.

11. …AND SO MIGHT OUR ANIMAL NATURE.

The 2013 study, conducted by a professor at Arizona State University, suggests that this revulsion with armpit hair may be a Western aversion to our primal roots as animals. Other animals send out chemical signals called pheromones to attract mates. We still don't know whether pheromones exist in humans, but plenty of evidence indicates we are highly sensitive to each other's biochemicals. If pheromones do exist, body hair around the groin and armpits could be a likely place to find them. But as "civilized" people, we believe the process of finding a partner lies in our hearts and minds—not in our armpits. Maybe one day we'll find out it's all of the above. 

12. YOUR ARMPIT LYMPH NODES MAY WARN YOU OF BREAST CANCER.

Most of the time a swollen lymph node in the armpit is little more than a sign of a cold or flu virus attacking your body. However, it can also be an early symptom of inflammatory breast cancer, an aggressive form of cancer that is best treated when caught as early as possible. Other areas that may swell in this cancer are your breast itself, and around your collarbone. If you have these kinds of sudden swellings, it's a good idea to see a doctor.

13. SOME PEOPLE GET THEIR ARMPITS BOTOXED.

A condition known as hyperhidrosis—excessive sweating—can be frustrating for those who'd like to be able to simply wear clothing they don't drench. According to Dr. Sonam Yadav, medical director of a cosmetic dermatology clinic in New Delhi, India, Botox is used to treat underarm sweating (yes, here in the U.S. too). Yadav tells Mental Floss, "It works by regulating the synergy between the neuromuscular junction and the sweat glands."

Why Do We Get Shivers Up Our Spines?

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iStock.com/martin-dm

Picture this: You're sitting on your couch in the dark alone, watching a scary movie. The killer is walking toward an unsuspecting victim, then suddenly jumps out at her. In that moment, the hairs on your body stand up, and you get a shiver down your spine. When you go for a walk on a crisp morning, the same thing happens. When the music swells during your favorite song, you get the shivers again, this time with the little goosebumps on your arms that appear when you get that sensation.

There's a good reason for shivers and goosebumps: they're your body's response to emotion or stress. We got this from our animal ancestors. When they were cold, the hair on their bodies would stand up—the movement of the arrector pili muscle would cause the skin to contract, raising each hair—to provide an extra layer of insulation. This response is also in play when animals feel threatened: their natural reaction is to try to look bigger than their attacker, so their skin and hair expand to play up that effect. The part of the brain called the hypothalamus is what controls this reaction.

So why do goosebumps—also known as cutis anserina or piloerection—appear, aside from the functional purpose of looking larger or creating insulation? It's because our emotions are also connected with the hypothalamus, so sometimes goosebumps are just our body reacting to our brain's signals of intense emotion.

When we feel things like love, fear, or sadness, the hypothalamus sends a signal to our bodies that produces adrenaline in our blood. The signal triggers the arrector pili muscles to contract, and then we have goosebumps caused by emotion. The sudden adrenaline rush may also cause sweaty palms, tears, increased blood pressure, or shivers.

When we listen to music and get shivers, it is a mixture of subjective emotions toward the music and physiological arousal. If we hear a song we get excited about, or a song that makes us sad, the hypothalamus reacts to the sudden change in emotion and we physically feel the shiver along our spine.

This article was republished in 2019.

10 Facts About the Lungs

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iStock/pixelfit

Every cell in your body needs oxygen in order to function properly. Your lungs are obviously crucial in achieving this goal—once you take air into your lungs, oxygen enters the bloodstream and moves through your body. Each cell makes a trade, exchanging oxygen for carbon dioxide—which your bloodstream then transports back to the lungs. When you exhale, you’re actually expelling carbon dioxide (CO2), nitrogen, and water vapor.

So how does your body make this happen? Bronchial tubes connect your lungs to your throat and mouth. These are lined with tiny little hairs called cilia that move in wave-like patterns, which pushes mucus up your throat. At the base of the bronchial tubes are tiny air sacs that hold the air you breathe in, called alveoli. Your right lung has three balloon-like sections, called lobes, which are full of spongy tissue. Your left lung has only two lobes, to make room for the heart. They sit in a special membrane called the pleura, that separates your lungs from the wall of your chest. Altogether, your lungs are a highly efficient machine—and they do a lot more than you might think.

1. Taking in oxygen is only one of your lungs' most important jobs. 

Yes, you need oxygen to live, but if you didn’t expel the carbon dioxide in your lungs, you would die. Carbon dioxide acts as an acid in the body and is generated by muscle action, Wendie Howland, a nurse with Howland Health Consulting, tells Mental Floss. “Your body operates optimally at a fairly narrow pH range, and when you generate extra CO2 by, say, running up the stairs, you bring your pH into the normal range almost immediately by excreting CO2 by breathing deeply.” So exhaling that more toxic CO2 is as important as taking in oxygen.

2. Think of your lungs as big ol' buckets.

Rather than thinking of your lungs as big balloons, Cascari says, “Think of your lungs as buckets of blood with air bubbles going through them.” In fact, your lungs contain as much blood as the entire rest of your body, which is why your center of gravity is above your waist. They produce blood cells as well. Every time your heart beats, it sends an equal amount of blood to your lungs as it does everywhere else in your body. “It’s this incredible system that can respire—an exchange of gas from the air into the blood and the lungs—without leaking. The fact that that goes on day in day out for our whole life is pretty amazing,” he says.

3. Your lungs are huge.

Your lungs are one of your biggest organs, but you might be surprised to learn that if you spread out the surface area of the alveoli, the sacs where oxygen and blood interface, you could cover an entire tennis court, Schroeder says.

4. Without mucus, your lungs would dry up. 

You may not be a big fan of mucus when it’s clogging your chest or nose during a cold, but it’s a “highly underrated, powerful infection-fighting agent in your body with some pretty cool features," says Ray Casciari, a pulmonologist at St. Joseph Hospital in Orange, California. “It’s actually cleaner than blood,” Casciari reveals. “If you take bacteria and expose it to mucus, the mucus will stop the growth of the bacteria. Whereas blood will actually support the growth of the bacteria.” (In fact, researchers in laboratories often deliberately use blood to grow bacteria.) Your mucus is such an important protective agent that you’d die without it. “If you didn’t have mucus in your lungs, you would dehydrate, losing so much water through evaporation that you would die within minutes,” he says. On the other hand, too much mucus production is dangerous.

5. Whatever you inhale quickly goes from your lungs to your brain. 

In under seven seconds, to be precise. Because of your lungs’ enormous surface area and “its intimate relationship with blood vessels that surround it,” says Scott Schroeder, director of Pediatric Pulmonary Medicine at the Floating Hospital of Tufts Medical Center, an inhalation of smoke or a vaporized medicine can reach the brain very quickly.

6. Coughing isn't always bad for your lungs.

Even when you aren’t sick, a normal person coughs about 10 times per day, says Schroeder—whether due to a sticky piece of food, an allergen you accidentally inhale, or your own mucus generated by exercise.

7. Asthma isn't just one disease affecting lung function.

Asthma, which causes wheezing, coughing, and shortness of breath, is actually a number of different illnesses under one name, Schroeder says. The good news is that deaths due to asthma are very uncommon, and have decreased significantly over the last 20 years, he reports (with one notable exception—African-American men age 18–24). But it doesn’t affect everyone equally. Women are much more likely to develop asthma as adults than men, especially if they are overweight. And people in urban areas are more likely to suffer from asthma than those in rural areas, likely due to increased particulate matter in the air from car exhaust and industrial pollutants.

8. Exercise can make asthma—and your lung function—better.

Asthma is actually improved by cardiovascular exercise. Schroeder says there are no sports that people with asthma cannot participate in, “except scuba diving, but I don’t consider that a sport.”

9. You can get lung cancer even if you've never smoked.

“You can spend your whole life in a very clean environment, never having smoked, and still get lung cancer,” Casciari says. Not all lung cancer is caused by cigarette smoking (though the majority is). Casciari cites occupational exposure, radiation exposure, and potential genetic risk factors, although researchers are still exploring the role genetics play. “Folks tend to think of their lungs very little, and when they do, they think, ‘I don’t smoke, so I’m ok,’ but that’s not completely true.”

10. Breakthroughs in lung cancer treatments has improved survival rates. 

For decades, toxic chemotherapy has been the best medicine for treating lung cancer, but it comes with intense side effects. However, several new breakthroughs have recently improved outcomes for patients, says Casciari. Thoracic CT scans, for example, improve survival by 20 percent by providing earlier diagnosis and treatments. Furthermore, new minimally invasive surgery techniques have made recovery from lung cancer surgery much easier, with people being discharged on the same day of surgery. Finally, immunotherapies that target specific cancer markers and harness the immune system itself to fight cancer cells have improved outcomes—and decreased side effects—for lung cancer patients.

This story was first published in 2017.

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