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."

Here’s What Happens to Your Body During Anaphylaxis

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According to the Centers for Disease Control and Prevention, allergies affect more than 50 million Americans every year—and anaphylaxis, the most severe allergic reaction, affects at least 1.6 percent of the general population [PDF]. Here’s the science of what happens to the body during anaphylactic shock.

ALLERGEN EXPOSURE

In a person with allergies, cells sometimes identify foreign but innocuous stimuli as major threats. Why some people are allergic to certain things while others are not is a mystery science hasn't yet solved, but we do know how it happens: through a process called sensitization.

Here’s how it works. When the body encounters a foreign substance, also called an antigen, immune system cells deliver some of substance's molecules to T-helper cells living in the lymph nodes. Those cells also bring along a type of molecule that informs a T-helper cell it’s time to stage an immune response. Known as a costimulatory molecule, it's necessary to activate any type of immune system reaction involving T cells, whether you have allergies or not.

Being exposed to an antigen "primes" a T-helper cell, turning it into a Th2 cell. Primed Th2 cells release proteins called interleukins, which do two things: First, they interact with another type of immune cell called B cells to produce infection-fighting antibodies that bind to mast cells, which contain chemical particles they'll release in the presence of an antigen. Second, the interleukins activate eosinophils, a type of white blood cell that discharges toxic substances to destroy invading cells (and, occasionally, host cells). In this process, the immune system identifies the "threat" and deploys cells prepared to fight it. The immune system's elevated level of awareness of and preparation against the antigen reclassifies the substance as an allergen—a considerably more dangerous threat.

Because an allergy only develops after this process, a person allergic to strawberries, for example, will only experience a reaction the next time they eat something containing strawberries. New allergies can pop up at any point in your life.

An immune system on allergies is a little bit like a brain that can't distinguish a piece of lint from a spider: unable to relax, constantly on guard against every potential threat. After initial exposure, the mast cells activated during the sensitization phase are still equipped with allergen-specific antibodies and remain combat-ready, prepared to respond immediately should a second exposure ever occur. If it does—and it probably will—here’s what you can expect to happen.

ALLERGIC REACTION

If two or more allergen molecules bind to a sensitized mast cell, the mast cell releases inflammatory mediators that produce an allergic reaction. These mediators include substances like histamine and more of the interleukins that, in turn, activate eosinophils, Th2 cells, and basophils (another type of white blood cell). In a non-allergic reaction, mediators produce helpful inflammation that prevents infection and initiates healing—but those same symptoms can be annoying and even dangerous when the immune system attacks an otherwise benign allergen. Mast cells also release leukotrienes, which recruit more immune cells to the area and speed up the reaction. That leads to what Stanford University researcher Tina Sindher calls a “‘chain reaction’ of allergic inflammation.”

With the release of histamine, you might experience both bronchial contraction—which makes it more difficult to breathe—and blood vessel dilation. The latter makes it easier for blood to flow to affected areas, but it also makes blood vessels more permeable, allowing blood to escape from the blood vessel walls and flow into the spaces between cells and causing swelling and hives.

For most, these symptoms are merely uncomfortable; they can occur as late as eight to 12 hours after initial exposure, long after the allergen is gone, and can be alleviated with an antihistamine like Benadryl. But for a person with severe allergies, a life-threatening allergic response can occur within minutes: Their airways will constrict so much they won't be able to breathe, and their blood vessels will be unable to contract, which can lead to a drop in a blood pressure and keep veins from getting blood back to the heart. The combination of airway constriction and blood vessel dilation can make it impossible for the body to supply enough oxygen to major organs—that's anaphylactic shock.

The only way to stop anaphylaxis in its tracks is with epinephrine, more commonly known as adrenaline. Adrenaline is a hormone naturally produced by the adrenal glands to help generate the "fight or flight" response in emergency situations. It works by constricting certain blood vessels, increasing blood pressure, and relaxing airways, counteracting all the reactions produced by histamines.

According to Sindher, it’s important to use epinephrine immediately if you're at risk for anaphylactic shock. “There’s a general belief out there that epinephrine should only be used in the worst-case scenario,” she tells Mental Floss. “In fact, most of the complications we see in food allergic reactions are due to delayed use in Epi. Antihistamines can be helpful in treating the symptoms of itching and congestion, but they do not help stop an allergic reaction.”

THE FUTURE OF ALLERGY TREATMENT

Researchers like Sindher are still trying to understand what causes allergies, and why the prevalence of food allergies has increased over the past few decades. Sindher’s main goal is to find new ways of treating (and hopefully curing) allergies. The most established technique (for food allergies, at least) is oral immunotherapy, where allergic individuals gradually eat more of their allergen until they can have small amounts without experiencing a reaction. That’s usually done extremely gradually, over the course of months or years, and always under the supervision of a certified allergist.

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Sindher says scientists are still testing other types of immunotherapy treatments and vaccinations in clinical trials: “A lot of research is going into trying to identify the causes so we can be successful in the prevention as well as treatment of food allergies.”

Until that happens, though, doctors say the best course of action is to be careful around allergens. Medications are useful and necessary, but prevention is the name of the game when it comes to allergies.

12 Facts About the Gallbladder

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Don't feel too bad if you forgot you have a gallbladder—it's one of those body parts that people tend to ignore unless there's a problem. Here's a refresher: It's that small pouch beneath the liver whose primary function is to store bile, which helps you digest fats. So the next time you wolf down a Quarter Pounder with cheese, you can thank your gallbladder for doing its part. Here are a few other things you should know.

1. IT’S THE SIZE OF A SMALL PEAR, AND IT LOOKS LIKE ONE, TOO.

Right before you take your first bite of pizza, your gallbladder is full of bile—an alkaline fluid that's produced in the liver, transported to the gallbladder, and then released into the small intestine to help break down fat and bilirubin, a product of dead red blood cells. The organ can hold the equivalent of a shot glass of the yellow-green liquid, which causes it to swell up to the size of a small pear.

When you eat certain foods—especially fatty ones—the gallbladder releases the bile and deflates like a balloon. Although most gallbladders are roughly 1 inch wide and 3 inches long, there are notable exceptions. In 2017, a gallbladder removed from a woman in India measured nearly a foot long, making it the longest gallbladder in the world.

2. YOU CAN LIVE WITHOUT IT.

You don’t need your gallbladder to live a full and healthy life. Just ask British playwright Mark Ravenhill, who wrote an account for the BBC about getting his gallbladder removed after a gallstone—a solid object made of cholesterol or calcium salts and bilirubin—had moved painfully into his pancreas. "'The gallbladder's completely useless,'" Ravenhill recalled his doctor explaining. "'If it's going to be a problem, best just to take it out.'"

In addition to preventing more gallstones from forming, a physician may recommend that a patient’s gallbladder be removed due to other diseases, like cholecystitis (inflammation of the gallbladder) and cancer. In most cases, removing it doesn’t affect digestion, but there can be some complications. "People can certainly live without one, but they do have to watch their fat intake," says Ed Zuchelkowski, an anatomist and biology professor at California University of Pennsylvania. People who don't have gallbladders still produce bile, but it flows directly from the liver to the small intestine. The only difference is that "you would not have as much bile readily available to release," Zuchelkowski tells Mental Floss, which could cause minor problems like diarrhea if you're eating fatty foods.

3. OUR HUNTER-GATHERER ANCESTORS MAY HAVE NEEDED IT MORE THAN WE DO.

"[The gallbladder] probably was more important to people in days when they would eat fewer meals and larger meals," Zuchelkowski says. This was generally the situation that our hunter-gatherer ancestors found themselves in. As Ravenhill notes, "feast or famine was the general rule." Nomadic groups ate large slabs of meat about once a week, and the gallbladder helped to quickly digest the onslaught of protein and fat.

Even though our diets and eating habits have changed drastically since then, evolution hasn't caught up—we still have the same digestive system. It's probably for this reason that "most meat-eating animals have a gallbladder," Zuchelkowski says. "Dogs do, cats do—they can concentrate bile just like we do, but I think you’d find that in animals that only eat vegetation, that’s where it’s likely to be missing.” However, Zuchelkowski notes that the gallbladder also helps you absorb fat-soluble vitamins like A, D, E, and K, so it still serves a useful function in people who are vegetarians.

4. ASTRONAUTS ARE ENCOURAGED TO GET THEIRS REMOVED.

A 2012 report from the Canadian Journal of Surgery recommended that astronauts consider having their appendix and gallbladder removed—even if their organs are perfectly healthy—to prevent appendicitis, gallstones, or cholecystitis from setting in when they’re far, far away from Earth's hospitals. “The ease and safety of surgical prophylaxis currently appears to outweigh the logistics of treating either acute appendicitis or cholecystitis during extended-duration space flight,” the authors wrote.

5. ALEXANDER THE GREAT LIKELY DIED FROM A GALLBLADDER GONE BAD.

Alexander may have been great at conquering entire empires, but his organs weren’t exactly up to the task. The king of Macedonia died at the age of 34, and some historians believe that the cause was peritonitis (inflammation of the peritoneum, the tissue lining the abdomen), which itself was a result of acute cholecystitis. “Historians have suggested that the fatal biliary tract disease was fueled by excess consumption of alcohol and overeating at a banquet that Alexander threw for his leading officers in Babylon,” author Leah Hechtman writes in Clinical Naturopathic Medicine.

6. THE DOCTOR WHO CONDUCTED THE FIRST SUCCESSFUL GALLSTONE REMOVAL SURGERY DIDN'T KNOW WHAT HE WAS LOOKING FOR.

Gallbladder-related ailments have been afflicting humans for thousands of years, as evidenced by gallstones found in Egyptian mummies. And for thousands of years, people put up with it because they didn’t know what was wrong or how to fix it. In fact, it wasn’t until 1867 that the first cholecystotomy (removal of gallstones) was carried out. The surgery was performed by Dr. John S. Bobbs of Indianapolis, who had no idea what ailed his patient, 31-year-old Mary Wiggins, until he cut open a sac that he later realized was her gallbladder and “several solid bodies about the size of ordinary rifle bullets” fell out, according to The Indianapolis Star. Amazingly, Wiggins survived and lived to the age of 77. Fifteen years after this surgery, the first cholecystectomy (removal of the gallbladder) was performed in Germany.

7. THE WORLD RECORD FOR MOST GALLSTONES EVER REMOVED FROM A PERSON'S BODY STANDS AT MORE THAN 23,000.

Unlike the Guinness World Record for most Twinkies devoured in one sitting, this isn’t the kind of record you’d enjoy setting. In 1987, an 85-year-old woman complaining of severe abdominal pain showed up at Worthing Hospital in West Sussex, England, and doctors found a shockingly high number of gallstones—23,530, to be exact. In May 2018, a similar (albeit less severe) case of gallstones was reported in India, where a 43-year-old man underwent surgery to have thousands of them removed. “Usually we get to see two to 20 stones, but here there were so many and when we counted them, it was a whopping 4100,” the surgeon told Fox News.

8. SOME EASTERN CULTURES BELIEVE THERE’S A LINK BETWEEN THE GALLBLADDER AND HEADACHES.

Some practitioners of Eastern medicine—especially Traditional Chinese Medicine (TCM)—purport that gallbladder problems can cause certain kinds of headaches. TCM practitioners say our internal organs are connected to channels called meridians, which direct several fundamental substances—like blood, other bodily fluids, and qi (vital life energy)—throughout the body. The gallbladder meridian, for instance, runs along the side of the head near the temple. Through the practice of acupuncture, tiny needles are inserted into the skin along the gallbladder meridian in an effort to relieve tension and free up blocked qi. (Western scientists tend to disagree on what, if any, benefit acupuncture offers.)

9. IN CHINA, BOLD PEOPLE ARE SAID TO HAVE A “BIG GALLBLADDER.”

Speaking of China, the country's primary language, Mandarin, hints at a link between organ function and personality. For instance, a word that’s assigned to bold and daring people translates to “big gallbladder,” and brave people are said to have “gallbladder strength,” according to The Conceptual Structure of Emotional Experience in Chinese. The word for coward, on the other hand, translates to “gallbladder small like mouse.” (Interestingly, mice do in fact have gallbladders, but rats don’t.)

10. WESTERN PHILOSOPHERS ALSO THOUGHT ONE'S TEMPERAMENT HAD TO DO WITH THE GALLBLADDER.

You may remember learning something about the four humors during a high school lesson on ancient Greece. The theory, originating with Hippocrates, held that a person’s temperament was influenced by one of four bodily fluids: black bile, yellow bile, phlegm, and blood. Yellow bile, stored in the gallbladder, was said to make people choleric, or irritable. Disease was blamed on an imbalance of these four humors, and this remained a popular theory up until the 18th century. Because of this theory's longstanding influence, the word gall—a synonym for bile—also meant “embittered spirit” during medieval times. It wasn’t until 1882 that the word took on the meaning of "impudence" or "boldness" in American English—as in “I can’t believe he had the gall to finish that Netflix series without me.”

11. ANCIENT ETRUSCANS USED THEM FOR DIVINATION.

Well, not human gallbladders. Ancient Etruscans, a group of people who once lived in present-day Tuscany and whose civilization became part of the Roman empire, practiced a type of divination called haruspicy. The soothsayers were called haruspices (literally “gut gazers”), and they looked for clues from the gods in the markings, coloring, and shape of a sacrificial sheep’s liver and gallbladder. This was often done before the Romans went into battle, but the practice was never adopted as part of the state religion.

12. SOME GALLBLADDERS SPORT A PHRYGIAN CAP.

A crease called a "Phrygian cap" at the base of the gallbladder occurs in about 4 percent of people. Its odd name is something of a misnomer. It comes from its resemblance to a type of peaked felt hat called a pileus, worn by emancipated slaves in ancient Rome; the design was similar to the peaked caps then worn in Phrygia, a region in modern-day Turkey. Much later, during the French Revolution, people took to wearing Phrygian caps—which they likely confused with the pileus's style—as symbols of their freedom from tyranny. In the 20th century, the Smurfs started wearing them.

As for the aforementioned gallbladder abnormality, there’s no deeper symbolism in its name. The way it folds over just looks a lot like a Phrygian cap. Despite being a “congenital anomaly,” as a 2013 study published in Case Reports in Gastroenterology puts it, the condition typically causes no symptoms or complications.

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