11 Facts About Fingernails

iStock
iStock

Whether there's dirt beneath them or polish atop them, your fingernails serve more than just decorative purposes: They help keep your fingertips safe and have a multitude of special functions that even your doctor might not be aware of. “The nails occupy a unique space within dermatology and medicine in general, particularly because they are such a niche area about which few people have expertise,” Evan Rieder, assistant professor in the Ronald O. Perelman Department of Dermatology at NYU Langone Health, tells Mental Floss.

1. FINGERNAILS HAVE FOUR MAIN PARTS.

Along with skin and hair, nails are part of the body's integumentary system, whose main function is to protect your body from damage and infection. Fingernails have four basic structures: the matrix, the nail plate, the nail bed, and the skin around the nail (including the cuticle).

Fingernail cells grow continuously from a little pocket at the root of the nail bed called the matrix. The pale, crescent-shaped lunula—derived from Latin for "little moon"—on the nail itself is the visible portion of the matrix. If the lunula is injured, the  nail won't grow normally (a scarred lunula can result in a split nail), and changes in the lunula's appearance can also be signs of a systemic disease.

Fingernail cells are made of a protein called keratin (same as your hair). As the keratin cells push out of the matrix, they become hard, flat and compact, eventually forming the hard surface of the nail known as the nail plate. Beneath that is the nail bed, which almost never sees the light of day except when there's an injury or disease.

Surrounding the matrix is the cuticle, the semi-circle of skin that has a tendency to peel away from the nail. The skin just underneath the distal end of the fingernail is called the hyponychium, and if you've ever trimmed your nails too short, you know this skin can be slightly more sensitive than the rest of the fingertip.

2. THEY GROW AT A RATE OF 0.1 MILLIMETERS A DAY ...

That's about 3 to 4 millimeters per month. But they don't always grow at the same speed: Fingernails grow more quickly during the day and in summer (this may be related to exposure to sunlight, which produces more nail-nourishing vitamin D). Nails on your bigger fingers also grow faster, and men's grow faster than women's. The pinky fingernail grows the slowest of all the fingernails. According to the American Academy of Dermatology, if you lose a fingernail due to injury, it can take up to six months to grow back (while a toenail could take as much as a year and a half).

3. ... BUT NOT AFTER YOU'RE DEAD.

You've probably heard that your fingernails keep growing after death. The truth is, they don't, according to the medical journal BMJ. What's actually happening is that the skin around the base of the fingernails retracts because the body is no longer pumping fluids into the tissues, and that creates a kind of optical illusion that makes the nails appear longer.

4. ITS ESTIMATED THAT 20 TO 30 PERCENT OF PEOPLE BITE THEIR NAILS.

Scientists say it's still unclear why, but they suspect nail-biters do it because they're bored, frustrated, concentrating, or because it just feels comforting (and anxiety doesn't seem to play a big role). Perfectionists who don't like to be idle are very likely to have the habit. Biters expose themselves to the dangerous crud that collects underneath the nail: The hyponychium attracts bacteria, including E. coli, and ingesting that through nail-biting can lead to gastrointestinal problems down the line. Biting can also damage teeth and jaws.

5. HUMAN FINGERNAILS ARE BASICALLY FLAT CLAWS.

Our primate ancestors had claws—which, like nails, are made of keratin. As human ancestors began using tools some 2.5 million years ago (or even earlier), evolutionary researchers believe that curved claws became a nuisance. To clutch and strike stone tools, our fingertips may have broadened, causing the claws to evolve into fingernails.

6. THE NAIL ACTUALLY MAKES YOUR FINGERTIP MORE SENSITIVE.

While the fingernail may be tough enough to protect tender flesh, it also has the paradoxical effect of increasing the sensitivity of the finger. It acts as a counterforce when the fingertip touches an object. "The finger is a particularly sensitive area because of very high density of nerve fibers," Rieder says.

7. FINGERNAILS CAN REVEAL LUNG, HEART, AND LIVER DISEASES.

"One of the most interesting facts about fingernails is that they are often a marker for disease within the body," Rieder says. Nail clubbing—an overcurvature of the nail plate and thickening of the skin around the nails—is a particularly significant sign of underlying illness, such as lung or heart disease, liver disease, or inflammatory bowel disease. Two-toned nails—whitish from the cuticle to the nail's midpoint and pink, brown, or reddish in the distal half—can be a sign of kidney and liver disease. Nails that are two-thirds whitish to one-third normal can also be a sign of liver disease. However, little white marks on your nails, known as milk spots (or punctate leukonychia) are just the remnants of any kind of trauma to the nail, from slamming it in a door to chewing on it too fervently.

8. YOU CAN GET A COMMON SKIN DISEASE ON YOUR NAILS.

Psoriasis is "typically thought of as a skin disease, but is actually a skin, joint, and nail disease, and when severe, a marker of cardiovascular risk," Rieder says. Psoriatic fingernails may have orange patches called oil spots, red lines known as splinter hemorrhages, lifting of the edges of the nails, and pits, "which look like a thumb tack was repeatedly and haphazardly pushed into the nails," he says.

Doctors often prescribe topical or injected corticosteroids to treat psoriatic nails, but using lasers is an emerging and potentially more cost-effective technique. Rieder relies on a pulsed dye laser, which uses an organic dye mixed with a solvent as the medium to treat nail psoriasis, "which can be both medically and aesthetically bothersome," he says. This laser is able to penetrate through the hard nail plate with minimal discomfort and "to treat targets of interest, in the case of psoriasis, blood vessels, and hyperactive skin," Rieder says.

9. ANCIENT CULTURES DISPLAYED SOCIAL STATUS WITH NAIL ART.

Painting and other forms of decorating nails have a history of offering social and aesthetic cues through variations in nail color, shape, and length, Rieder says. In fact, he adds, in some cultures ornate and well-decorated fingernails "serve as a proxy for social status."

Five thousand years ago in China, men and women of the Ming Dynasty aristocracy grew their nails long and covered them with golden nail guards or bright home-made polishes. The long nails allegedly announced to the world their social rank and their freedom from performing menial labor.

10. A FORMER BEAUTICIAN HELD THE WORLD RECORD FOR THE LONGEST NAILS.

Lee Redmond of Utah started growing her nails in 1979 and kept at it until she held the world record for "longest fingernails on a pair of hands ever (female)" in 2008. Her right thumbnail was 2 feet, 11 inches and the collective length of all her nails was 28 feet, 4 inches. She also applied nail hardener daily and painted them a reflective gold. Unfortunately, she broke her nails in a 2009 car accident and has no plans to regrow them.

More recently, the man who holds the Guinness record for the "longest fingernails on a single hand—ever" chose to chop them off at Ripley's Believe It Or Not! in New York City in July 2018. Shridhar Chillal of Pune, India started growing the nails of his left hand in 1952, when he was 14 years old. At last count, the total length measured 29 feet, 10.1 inches.

11. THE FIRST NAIL CLIPPERS WERE PATENTED IN 1875.

Today, biters don't have to use their teeth to trim their nails. While the earliest tools for cutting nails were most likely sharp rocks, sand, and knives, the purpose-built nail clipper—though it might be more accurately called a circular nail file—was designed by a Boston, Massachusetts inventor named Valentine Fogerty and patented in 1875. The nail clippers we know today were the design of inventors Eugene Heim and Oelestin Matz, who were granted their patent for a clamp-style fingernail clipper in 1881.

14 Facts About Feet

iStock/pepifoto
iStock/pepifoto

The foot is one of the most overworked, under-appreciated parts of the human body. Think about it: In a single day, the average person takes 8000 to 10,000 steps. That works out to be four trips around the world over a lifetime, putting a lot of wear and tear on your intricate foot bones. The foot may be humble, but its design is essential to how we walk upright, and hoofing it on two feet is a defining feature of humanity. Here are some fun—and a few funky—facts about the human foot.

1. FOOT BONES MAKE UP ABOUT A QUARTER OF ALL THE BONES IN OUR BODIES.

There are 26 foot bones in each of your feet—one less than in each hand. When we’re born, those foot bones are mostly cartilage. They only completely harden around age 21.

2. HUMANS HAVE WORN SHOES FOR A VERY LONG TIME.

When did humans begin wearing shoes, anyway? About 40,000 years ago, according to research from Washington University in St. Louis that analyzed foot bones from Neanderthals and early humans. Older specimens had thicker, stronger toes, likely from gripping the ground as they walked barefoot. That’s around the same time that the archaeological record shows a burst of artistic and technological advancements among early humans, including the first stone tools, which may have aided in the production of shoes. The oldest preserved shoe, incidentally, is 5500 years old and was found in an Armenian cave, buried in sheep dung.

3. THE BIG TOE USED TO BE A KIND OF FOOT THUMB.

This grasping toe helped our predecessors climb trees and, when young, grip onto their mothers. Thanks to modern science, if you lose your thumb, you can now replace it with a toe: toe-to-thumb transplants are a surprisingly common procedure these days.

4. FOOT BONES HOLD BIG CLUES ABOUT THE EVOLUTION OF BIPEDALISM.

Scientists are studying Homo naledi, a specimen discovered in a South African cave in 2013 that many researchers believe is a new human relative. H. naledi had very human-like feet, but with somewhat curved toe bones that suggest it climbed trees. It could be that H. naledi was beginning to experiment with walking. 

5. THERE WAS A FOOT CHEESE EXHIBITION IN IRELAND.

Warm, sweaty feet make a perfect home for bacteria, which feed on our dead skin cells and produce gases and acids that emit those arresting foot odors. They're apparently also good at cultivating cheese. An exhibition in Dublin in 2013 displayed a variety of cheeses made with bacteria samples obtained from real people’s feet, armpits, and belly buttons. Delicious. (No one actually ate any of the cheeses.)

6. FEET ARE ONE OF THE MOST TICKLISH PARTS OF THE BODY.

There’s a good reason for that: Humans have nearly 8000 nerves in our feet and a large number of nerve endings near the skin. Having ticklish feet can be a good sign: Reduced sensitivity can be an indicator of peripheral neuropathy (numbness in the feet caused by nerve damage). 

7. FOOT NUMBNESS CAN CAUSE BIG PROBLEMS FOR DIABETICS.

Complications of diabetes include poor circulation and foot numbness that can lead to serious skin ulcers, which sometimes require amputation of toes or feet. In 2010 alone, 73,000 lower-limb amputations were performed on diabetics.

8. FOOT SIZES AND WIDTHS IN THE U.S. AND UK ARE INCREASING.

Feet are spreading to support extra weight as our populations pack on the pounds. According to a 2014 study by the College of Podiatry in the UK, the average foot has increased two sizes since the 1970s. As people have grown taller and heavier, feet respond by growing. It appears many people are still in denial about their expanding feet: Though retailers are starting to respond by making larger and roomier shoes, half of women and a third of men reported they buy poorly fitting shoes. Podiatrists say ill-fitting shoes are to blame for a significant portion of foot problems, especially among women.

9. MANY GLAMOROUS CELEBRITIES HAVE BIG FEET.

From the bound feet of female Chinese elites to Cinderella and Barbie, freakishly small feet are often celebrated as more feminine. But plenty of glamorous women both past and present have had larger than average feet, among them Jacqueline Kennedy, Oprah Winfrey, Uma Thurman, and Audrey Hepburn (size 10, 11, 11, and 10.5, respectively).

10. WOMEN HAVE FOUR TIMES AS MANY FOOT PROBLEMS AS MEN.

That painful fact is often attributed to wearing heels. Ironically, Western women started wearing heels to effect a more masculine look: European men adopted the look from Persian warriors in the 17th century, and women soon followed suit.

11. THE AVERAGE PERSON WALKS ABOUT 100,000 MILES IN A LIFETIME. 

That’s a lot of stress on our feet. It’s not surprising, then, that lower back pain, headaches, indigestion, and spine misalignment are often related to foot problems. Some runners blow way past this mark: They've logged at least 100,000 in running miles alone. One committed runner, Herb Fred, has run a whopping 247,142 miles.

12. FOOT SIZE HAS ZERO TO DO WITH PENIS SIZE.

In a study published in 2015, researchers synthesized data from 17 previous studies that included the penis measurements of more than 15,000 men from around the world. The results: There is little evidence that penis size is linked to height, body mass, or shoe size.

13. THERE'S A REASON GRANDPA'S TOENAILS LOOK LIKE THAT.

Ever heard someone describing their toenails as “horse hooves”? As we get older, our toenails tend to thicken, making them hard to trim. This happens because toenails grow more slowly as we age, causing the nail cells to accumulate. Stubbing toes, bad shoes, and dropping things on your feet can also cause thickening, as can fungal infections and peripheral arterial disease, which narrows arteries and reduces the blood flow to limbs.

14. THERE'S A GUINNESS WORLD RECORD FOR MOST FEET AND ARMPITS SNIFFED.

Odds are you don’t have any job-related tasks nearly as revolting as this one: In the 15 years that Madeline Albrecht worked for an Ohio lab that tests Dr. Scholl products, she sniffed more than 5600 feet and untold numbers of armpits. Albrecht currently holds the Guinness World Record for—yes, this is a category—the number of feet and armpits sniffed.

11 Insightful Facts About Eyes

iStock.com/Paffy69
iStock.com/Paffy69

There are a lot of myths and misconceptions about the eyes. No, sitting too close to the TV won't damage your vision, and reading in dim light won’t hurt either. It’s understandable that various parts of the eye are so little understood, though. Each eye has more than a million optic nerve cells and over 106 million photoreceptor cells, making it one of the most complex organs we have. Here are a few more things you should know about your “windows to the soul.”

1. Newborn babies see the world in black and white—and red.

“It is a myth that babies see in black and white,” Anna Franklin, leader of the University of Sussex's Baby Lab, told The Guardian. While newborns do see black, white, and shades of gray, they can also detect red objects against a gray backdrop, Franklin says. The reason why they can’t see more colors is because the cones in their eyes—the photoreceptor cells responsible for picking up colors—are too weak to detect them. Those cells quickly get stronger, though. After about two months, babies can distinguish between red and green, and a few weeks later they can tell the difference between blue and yellow.

2. Your eyeballs grow as you age.

Another common misconception is that your eyes remain the same size from birth to adulthood. As a newborn, your eyes measure about three-fifths of an inch from front to back, compared to a little under an inch in adults. Your eyes actually grow a great deal in the first two years of life, and another growth spurt occurs when you go through puberty. The confusion likely stems from the fact that your eyes as a 6-month-old infant are two-thirds the size they will be when you’re an adult.

3. The length of your eye partly determines how well you'll be able to see.

If your eyeball is too long or too short, you might end up having problems with your vision. Nearsighted people have eyes that are longer than average, while farsighted people have eyes that come up a little short. If you were to magically add or remove a millimeter of length from your eye, it would completely change your prescription. Aside from eye length, the shape of your cornea (the outer part of the eye where contact lenses are placed) and lens (the part of the eye located behind the iris and pupil) are other key factors that determine the quality of your vision. That's because both of these parts work together to refract light.

4. Contact lenses can't really get lost behind your eye.

Although it may feel like a dislodged contact lens is stuck behind your eye, that isn’t exactly what’s happening. The thin membrane covering the white part of your eye and the underside of your eyelid—called the conjunctiva—forms a pouch and prevents objects from getting behind your eyeball. If a contact lens gets shifted out of place to the point where you can no longer see it, it’s just stuck underneath your upper eyelid, which isn’t nearly as scary.

5. Blue-eyed people share a common ancestor.

Originally, everyone in the world had brown eyes. It wasn’t until around 6000 to 10,000 years ago that the first blue-eyed person was born as a result of a genetic mutation, according to a 2008 study. That mutation of the OCA2 gene essentially “turned off the ability to produce brown eyes” and diluted the color to blue, Professor Hans Eiberg of the University of Copenhagen said in a statement.

6. Parts of the eye can get sunburned.

There’s a good reason you should wear sunglasses when it’s bright outside. Too much exposure to UV rays can damage the surface of the cornea and conjunctiva, causing a condition akin to sunburn called photokeratitis. Symptoms include pain, red or swollen eyes, the sensation of a foreign body in the eyes, blurred vision, headaches, and seeing halos around lights. While the discomfort is temporary and tends to go away within 48 hours, longer exposure to UV rays can have a long-term effect on your vision and lead to macular degeneration (deterioration of the retina, which is often age-related) and cataracts (clouding of the eye's lens, which reduces the amount of light coming in).

7. Your eye muscles are the fastest muscle in your body.

Extraocular muscles are what let you look around in all directions. You have six of these muscles in each eye, and many of the motions they make are involuntary. This lets you flick your eyes to one side and notice something in your peripheral vision without consciously looking in that direction. When both of your eyes move in the same direction, the movement is called a saccade, which comes from the French word for “jerk” (the verb, not the person). These jerky movements are extremely rapid, lasting about 50 to 60 milliseconds per saccade, according to Dr. Reza Shadmehr, professor of biomedical engineering and neuroscience at Johns Hopkins University. “Saccadic eye movements are the fastest voluntary movements that we can make. The eyes move at around 500 degrees per second or more,” Shadmehr tells Mental Floss.

8. Your eye movements might give away your next move.

Shadmehr and other researchers conducted an experiment in 2015 to test the relationship between saccades and decision-making. Participants were placed in front of a computer and asked to choose between two options that appeared on the screen: an immediate reward and a delayed reward. For instance, one option might be “get $10 today,” while the other might be “wait 30 days and get $30.” Their eye movements were tracked the entire time, and researchers discovered that these movements gave away the choice they were about to make before they made it. At the last minute, their eyes would move at a faster velocity towards the option that they preferred.

“What’s interesting is that as the saccades are being made, the velocity of the eyes starts out being equal between these two stimuli, but then right before you decide ‘I like A better than B,' the saccade that you make toward A has a higher velocity than the one you make toward B,” Shadmehr explains. “The idea is that the way you’re evaluating things is reflected in the way you move toward them.”

In another experiment, Shadmehr found a correlation between faster eye movements and impatient and impulsive behaviors. Similarly, other studies have shown that our eye movements are linked to moral decisions and even our political temperament.

9. You can tell some animals' place in the food chain by looking at a part of their eye.

In 2015, vision scientist Martin Banks and his colleagues looked at the eyes of 214 species in an attempt to answer the question, “Why do animal eyes have pupils of different shapes?” By the end of their study, they noticed a few patterns. Predatory animals like big cats and snakes tend to have pupils in the shape of vertical slits. This particular shape gives them the advantage of being able to accurately judge the distance separating them and their prey, so they'll know exactly how far they have to pounce. On the other hand, horizontal pupils are more common in goats, deer, cattle, and other herbivores. This shape improves an animal’s panoramic vision, which helps them look out for predators.

10. An eye condition may have been partly responsible for Leonardo da Vinci's artistic genius.

Visual neuroscientist Christopher Tyler argued in a recent paper that the master artist behind Mona Lisa had strabismus, a disorder where the eyes are misaligned. Essentially, one of his eyes turned outwards, and he was able to use both of his eyes separately (monocular as opposed to binocular vision). Tyler believes this actually aided his art by improving his ability to render three-dimensional images on a flat canvas. “The condition is rather convenient for a painter, since viewing the world with one eye allows direct comparison with the flat image being drawn or painted,” Tyler said. We’ll never know for sure whether or not this was true for Leonardo, but it’s an intriguing theory.

11. SURGEONS HOPE TO BE PERFORMING WHOLE EYE TRANSPLANTS BY 2026. 

Currently, only cornea transplants to improve vision are possible, but a team of Pittsburgh-based transplant surgeons said in 2016 that they hoped to be performing whole eye transplants in humans within the next decade. Transferring an eye from a deceased donor to a recipient certainly won’t be easy, though. A complicated network of muscles, blood vessels, and nerves connects the eyes to the brain via the optic nerve. However, further studies into the optic nerve and recent advances in immunosuppressive drugs and surgical techniques have brought them several steps closer to achieving this goal. If successful, the surgery could restore vision to people who have suffered severe eye injuries. Their research is backed by the Department of Defense, which is concerned about the number of soldiers who sustain eye injuries in combat.

SECTIONS

arrow
LIVE SMARTER