26 Fascinating Facts About the Human Body

Ridofranz/iStock via Getty Images Plus
Ridofranz/iStock via Getty Images Plus

You may not think about it very often, but there's so much to learn about the human body. For instance, did you know that people are actually covered in invisible stripes? In this article, which was adapted from an episode of The List Show, we take a look at some fascinating facts about the human body you might not know.

1. Only humans have chins.

Humans are the only animals with chins. While you may think every animal has one, that’s just what we tend to call the bottom of the head. But in reality, a chin is a very specific bone feature that extends forward from the lower jaw. Some experts propose that elephants and manatees have chins, but others argue that they’re such fundamentally distinct structures they shouldn’t be compared to humans. Experts still aren’t sure why people evolved to have chins; the reason might have to do with eating or speaking, or they may just have emerged as a side effect from some other useful feature.

2. Humans have a strange bone called the hyoid.

A peculiar bone humans have is the hyoid. This is the one bone that doesn’t form a joint with another bone. Instead, it’s connected to muscles and ligaments. The hyoid sits between the jaw and the voice box and it’s used to keep all the lower mouth muscles in place. It also helps with swallowing and talking.

3. People that have more hair and innie belly buttons are more prone to lint.

Hairy people with innie belly buttons are more prone to belly button lint, which comes from fibers that rub off of clothing over time. Your stomach hair grabs onto the fibers and pulls them into your belly button.

Starting in 2011, a group of scientists started the Belly Button Biodiversity Project to learn about what's going on inside these little caves of mystery, and as it turns out, it's quite a lot. Samples from about 60 people revealed over 2300 total species of bacteria. And of those, only eight were identified as common, appearing in over 70 percent of belly buttons.

4. While it varies person to person, fingernails grow faster than toenails.

Your fingernails grow faster than your toenails. Though it varies from person to person, typically, fingernails grow about a tenth of a millimeter each day, while toenails grow at around half that pace. There’s a correlation between nail growth speed and the length of the nearest bone. This means that your longest fingers have faster-growing nails than your shorter fingers.

5. Fingernails grow faster on your dominant hand.

Your fingernails grow faster on the hand that you write with. No one knows why.

6. As you age, your nails change.

Specifically, they grow more slowly and then nail cells, known as onychocytes, start accumulating. That’s why older people have thicker toenails. Fingernails aren’t as noticeably different because people manage them better, plus our toes endure a lot of damage throughout our lives.

7. It's a misconception that people's hair and nails continue to grow after they die.

What’s actually happening is the skin dehydrates and then recedes. So it looks like the hair and nails are getting longer, but in reality it's actually the skin that's getting shorter.

8. Breastfeeding will not cause breasts to sag.

It's a common misconception that breastfeeding causes breasts to sag. Pregnancy itself might affect breasts in that they may stretch and then recover differently. But research on breastfeeding confirms it will not cause breasts to sink. A behavior that will, though, is smoking.

9. Hands and feet contain over half the bones in an adult body.

With around 27 bones in each of your daddles—that’s an old slang word for the hands—and about 26 bones in each of your plates of meat—which is another old slang term for feet—these appendages account for over half of an adult’s bones, of which there are around 206 total. But that’s not always true. Feet mostly contain cartilage at birth, then bones form over time. They don’t fully harden until humans are in their early twenties.

10. You can fracture a rib just by sneezing.

While it's rare, it is possible to fracture a rib by sneezing. In 1885, there was an article in the Journal of the American Medical Association about a 72-year-old man who fractured his eighth rib while sneezing. Sneezer, by the way, is a 1940s Australian slang term meaning “excellent, wonderful,” which could definitely describe a good sneeze—but probably not one that would break a rib.

11. You can see stars if you rub your eyes.

If you've ever seen stars while rubbing your eyes, you’re not imagining it. The cells in our eyes are interpreting the pressure as an input, and treat that the same way they’d treat a light input.

12. Goosebumps are pretty much useless.

Goosebumps are frequently associated with adrenaline being released in the body, like when we’re feeling a particularly strong emotion, for example. They used to be important when people had way more hair on their bodies because goosebumps would elevate that hair and make a person look bigger when they were in danger. But now, they’re a pretty useless feature.

13. Spleens help the immune system.

The spleen is surprisingly not totally useless even though that was the belief up until the 1950s. It’s OK to get your spleen removed, but it does assist the immune system. While blood is in the spleen, the immune system creates the necessary antibodies to fight bacteria in that blood. A fetus’s spleen also creates red blood cells.

14. The appendix seems to help the immune system.

It's OK to get your appendix removed, but the organ also aids the immune system. In 2018, Dr. Mohamad Abouzeid, assistant professor and attending surgeon at NYU Langone Health told Mental Floss, "[The appendix] has a high concentration of the immune cells within its walls." Experts don't know exactly how the appendix affects the immune system, but it seems to play some role in keeping us healthy.

15. A fetus's face forms in the first three months after conception.

During the first three months after conception, a fetus’s face comes together, fusing in the area of the top of the lip. That means the dent under the nose, which is called the philtrum, is evidence of a person's time in the womb.

16. Babies don’t just see in black and white.

A newborn baby has pretty terrible vision. But it’s not true that they can only see in black and white. In reality, if there’s a large amount of the color red, they can identify it, but only if it appears in front of gray. Newborns have about 5 percent of the visual acuity that adults do, but it improves quickly and takes only around six months before they can see about as well as a grown-up. Though there are some eye tests that babies can school adults on, which are ones centered around subtlety. For example, up until 6 months old, a baby can tell monkeys apart, while older babies and adults can’t do that.

17. The liver is very good at regenerating itself.

In fact, with just 25 percent of the original liver tissue, it can regenerate. Liver transplants are generally only needed if someone has experienced severe damage to the organ or an injury.

18. Some people are born with three kidneys.

Some people had a kidney split while they were still in the womb, so they're actually born with three. This makes them prime candidates for donation, but the problem is people often don't know when they have three kidneys.

19. A person's large intestine can be stretched 5 feet and the small intestine can stretch 20 feet.

The intestines are pretty long: The small intestine stretches to about 20 feet and the large intestine hits 5 feet. The surface area of your intestines could take up two entire tennis courts, although some Swedish researchers have downgraded it to studio apartment size. Compare that with a blue whale, though, which has over 700 feet worth of intestines.

20. The stomach can hold up to 50 fluid ounces.

The stomach may not be tennis court size, but it can hold around 16 to 50 fluid ounces. It's interesting to note that a Trenta size at Starbucks is 31 fluid ounces, which is more than many adult stomachs can technically hold.

21. The neurotransmitter serotonin can be found in the gut.

Our gut contains 95 percent of the neurotransmitter serotonin. In fact, the gut, with its 100 million neurons, is so important to mood that it’s sometimes called the “second brain.” Medications that affect serotonin will often also cause GI issues.

22. The skin is the largest organ.

The skin is considered an organ and it's the body's largest one. An adult may have 22-square feet of skin on their body. Basically that means your skin could comfortably stretch across half the floor of the typical bathroom.

23. The skin makes up a large part of your body weight.

Fifteen percent of your total body weight, to be exact.

24. The ovaries are in communication with the brain.

It was once believed that the ovaries and uterus sort of sat dormant until they were needed, but the ovaries actually communicate with the brain in ways we’re just learning about. The hypothalamus and ovaries work together to make sure that the levels of hormones in the ovaries, like estrogen and progesterone, are where they need to be.

25. Humans are covered in stripes.

The human body is covered in stripes called Blaschko’s Lines, which are typically invisible. They’re cellular relics of our development from a single cell to a fully formed human.

26. Humans glow, but our eyes aren't able to detect it.

Humans glow, but it’s just around 1000 times weaker than our eyes can detect. Every animal that has metabolic reactions glows because in that process, photons get emitted, causing light. In 2009, a study was published in which a camera captured the bioluminescence of five men. According to that study, our upper body lights up the strongest. And the glow is on a cycle; when we’re on a normal sleep schedule, our bioluminescence is at its strongest at about 4 p.m.

10 Rad Gifts for Hikers

Greg Rosenke/Unsplash
Greg Rosenke/Unsplash

The popularity of bird-watching, camping, and hiking has skyrocketed this year. Whether your gift recipients are weekend warriors or seasoned dirtbags, they'll appreciate these tools and gear for getting most out of their hiking experience.

1. Stanley Nesting Two-Cup Cookset; $14

Amazon

Stanley’s compact and lightweight cookset includes a 20-ounce stainless steel pot with a locking handle, a vented lid, and two insulated 10-ounce tumblers. It’s the perfect size for brewing hot coffee, rehydrating soup, or boiling water while out on the trail with a buddy. And as some hardcore backpackers note in their Amazon reviews, your favorite hiker can take the tumblers out and stuff the pot with a camp stove, matches, and other necessities to make good use of space in their pack.

Buy it: Amazon

2. Osprey Sirrus and Stratos 24-Liter Hiking Packs; $140

Amazon

Osprey’s packs are designed with trail-tested details to maximize comfort and ease of use. The Sirrus pack (pictured) is sized for women, while the Stratos fits men’s proportions. Both include an internal sleeve for a hydration reservoir, exterior mesh and hipbelt pockets, an attachment for carrying trekking poles, and a built-in rain cover.

Buy them: Amazon, Amazon

3. Yeti Rambler 18-Ounce Bottle; $48

Amazon

Nothing beats ice-cold water after a summer hike or a sip of hot tea during a winter walk. The Yeti Rambler can serve up both: Beverages can stay hot or cold for hours thanks to its insulated construction, and its steel body (in a variety of colors) is basically indestructible. It will add weight to your hiker's pack, though—for a lighter-weight, non-insulated option, the tried-and-true Camelbak Chute water bottle is incredibly sturdy and leakproof.

Buy it: Amazon

4. Mappinners Greatest 100 Hikes of the National Parks Scratch-Off Poster; $30

Amazon

The perfect gift for park baggers in your life (or yourself), this 16-inch-by-20-inch poster features epic hikes like Angel’s Landing in Zion National Park and Half Dome in Yosemite National Park. Once the hike is complete, you can scratch off the gold foil to reveal an illustration of the park.

Buy it: Amazon

5. National Geographic Adventure Edition Road Atlas; $19

Amazon

Hikers can use this brand-new, updated road atlas to plan their next adventure. In addition to comprehensive maps of all 50 states, Puerto Rico, Canada, and Mexico, they'll get National Geographic’s top 100 outdoor destinations, useful details about the most popular national parks, and points on the maps noting off-the-beaten-path places to explore.  

Buy it: Amazon

6. Adventure Medical Kits Hiker First-Aid Kit; $25

Amazon

This handy 67-piece kit is stuffed with all the things you hope your hiker will never need in the wilderness. Not only does it contain supplies for pain, cuts and scrapes, burns, and blisters (every hiker’s nemesis!), the items are organized clearly in the bag to make it easy to find tweezers or an alcohol wipe in an emergency.

Buy it: Amazon

7. Hiker Hunger Ultralight Trekking Poles; $70

Amazon

Trekking poles will help increase your hiker's balance and stability and reduce strain on their lower body by distributing it to their arms and shoulders. This pair is made of carbon fiber, a super-strong and lightweight material. From the sweat-absorbing cork handles to the selection of pole tips for different terrain, these poles answer every need on the trail. 

Buy it: Amazon

8. Leatherman Signal Camping Multitool; $120

Amazon

What can’t this multitool do? This gadget contains 19 hiking-friendly tools in a 4.5-inch package, including pliers, screwdrivers, bottle opener, saw, knife, hammer, wire cutter, and even an emergency whistle.

Buy it: Amazon

9. RAVPower Power Bank; $24

Amazon

Don’t let your hiker get caught off the grid with a dead phone. They can charge RAVPower’s compact power bank before they head out on the trail, and then use it to quickly juice up a phone or tablet when the batteries get low. Its 3-inch-by-5-inch profile won’t take up much room in a pack or purse.

Buy it: Amazon

10. Pack of Four Indestructible Field Books; $14

Amazon

Neither rain, nor snow, nor hail will be a match for these waterproof, tearproof 3.5-inch-by-5.5-inch notebooks. Your hiker can stick one in their pocket along with a regular pen or pencil to record details of their hike or brainstorm their next viral Tweet.

Buy it: Amazon

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Adorable Products You Can Buy for International Sloth Day

Amazon
Amazon

It’s that time of the year again, folks—the time when we all collectively lose our chill over a slow-moving, two- or three-toed mammal with an adorable squeak and poop that defies physics. That’s right: International Sloth Day is on October 20. Here’s a list of must-have coloring books, onesies, and Christmas sweaters that you can pick up to showcase your love of one of the internet's favorite animals.

1. Cuddly Microwaveable Sloth; $20

Intelex/Amazon

Warm your heart and your body with a plush sloth that doubles as a soothing heating pad. The toy is filled with millet grains and dried French lavender, a combination intended to help you get to sleep easier.

Buy it: Amazon

2. Hanging Ceramic Sloth Planter; $18

FattyBee/Amazon

This flower planter pulls double duty, communicating both your love of sloths and your appreciation for plants. And it makes a tasteful piece of hanging home decor, too.

Buy it: Amazon

3. Sloth Coloring Book; $7

CreateSpace Independent Publishing Platform/Amazon

Sloths themselves are already works of art, but you’d be forgiven for wanting a few more sloth-related crafts in your life. Now you can make your own masterpiece with this detailed coloring book. All you'll need are some colored pencils and you'll be ready to go.

Buy it: Amazon

4. Farting Sloth Coloring Book; $7

M & L Coloring Books/Amazon

But maybe traditional coloring books aren’t your thing. You’re in luck: Amazon sells a coloring book for the crowd that both loves sloths and laughs a little too much at farts.

Buy it: Amazon

5. Sloth Socks; $14

Good Luck Socks/Amazon

These socks are ideal for people who might not want to wear their love of sloths out in the open but are very comfortable showing it off on their ankles.

Buy it: Amazon

6. Sloth Onesie; $40

Tipsy Elves/Amazon

No list of sloth-related products would be complete without a cozy onesie, and this one from Tipsy Elves is perfect for either pajamas or a last-minute Halloween costume. This onesie even comes with zippered pockets and cuddly sloth claws!

Buy it: Amazon

7. Sloth-Themed Ugly Christmas Sweater; $69

Tipsy Elves/Amazon

Why not celebrate the upcoming holiday season with this sloth-themed ugly Christmas sweater? You’re sure to be the hit of any holiday pub crawl or office Christmas party.

Buy it: Amazon

8. Sloth Mug; $10

LOZACH/Amazon

Embrace your inner sloth and declare your lazy feelings along with your morning cup of coffee.

Buy it: Amazon

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This article contains affiliate links to products selected by our editors. Mental Floss may receive a commission for purchases made through these links.