Here are 50 facts from FunFact's “Human body” topic, all checked. Each one cites its source (nih.gov, loc.gov, my.clevelandclinic.org…) and the date it was checked. This topic is part of FunFact Premium.
The chemical makeup of tears changes dramatically depending on whether you're cutting an onion or crying from sadness.
Emotional tears contain extra stress hormones, suggesting that crying literally helps release tension from the body.
Source: American Academy of Ophthalmology — Types of Tears · Checked on October 24, 2026
Kikunae Ikeda isolated glutamate from kombu seaweed and coined the word “umami,” which means “delicious” in Japanese.
It is found in Parmesan, soy sauce, ripe tomato and even breast milk. Its receptor was only identified in the early 2000s, which confirmed umami as a basic taste.
Source: Google Arts & Culture — Who found umami? · Checked on October 24, 2026
A 2009 study of 60 newborns: French babies tend to cry on a rising melody, German babies on a falling one.
The fetus hears its mother’s voice during the last months of pregnancy and retains its melody. The study compares group averages: you can’t guess the nationality of a particular baby by listening to its cry.
Source: Current Biology (Mampe et al., 2009), via ScienceDaily · Checked on October 24, 2026
The photoreceptors are at the back of the retina, behind the nerve cells and blood vessels, facing away from the light.
Octopuses have a retina wired the other way around and no blind spot. In us, the nerve fibers pass through the retina to form the optic nerve, which creates the blind spot. The brain corrects the image.
Source: NYU — Perception Lecture Notes: The Retina · Checked on October 24, 2026
The notion that a person is purely “logical” or “creative” depending on one hemisphere is a common misconception.
Although some functions are located mostly on one side, complex tasks require a constant, massive exchange of information between the two halves of the brain.
Source: Journal of Neuroscience — Brain Hemispheres Myth · Checked on October 24, 2026
12/8 corresponds to 120/80 mmHg: the unit comes from the old mercury-column blood pressure monitors.
In France, people often say “12/8” or “14/9,” whereas the rest of the world says 120/80 or 140/90 (in millimeters of mercury). The first number is the pressure when the heart contracts, the second when it relaxes.
Source: Futura — Pression artérielle et pression sanguine · Checked on October 24, 2026
In a 2004 study, two nights of shortened sleep lowered leptin by 18%, raised ghrelin by 28% and hunger by 24%.
The study covered only 12 young men. Hunger rose mostly for sugary, high-calorie foods (+33 to 45%). It shows a link between lack of sleep and appetite, not an identical effect for everyone.
Source: Annals of Internal Medicine (Spiegel et al., 2004) · Checked on October 26, 2026
Aδ fibers transmit sharp pain at 5-30 m/s; C fibers, which are slower (0.5 to 2 m/s), carry diffuse, burning pain.
For a bumped toe, the speed difference creates a noticeable delay: the sharp “ouch!”, then the throbbing pain. The longer the path to the brain, the clearer the delay.
Source: The Journal of Clinical Investigation — Nociceptors: the sensors of the pain pathway. · Checked on October 24, 2026
An Australian Antarctic base advises avoiding sweating “at all costs,” because damp clothing freezes in the outer layers.
As soon as you stop moving, sweat chills the body, with a risk of hypothermia. Hence the layering system: you take layers off as soon as you feel warm and put them back on when you stop.
Source: Australian Antarctic Division · Checked on October 26, 2026
This photic sneeze reflex seems to run in families and is harmless.
It is also called ACHOO syndrome, a humorous English acronym. Its exact mechanism is unknown: the most cited hypothesis is a “short circuit” between the optic nerve and the trigeminal nerve, which is close to the nose.
Source: scienceline.org — Why do some people sneeze when they look at the sun? · Checked on October 24, 2026
The unique patterns on our hands are etched before the baby is even born.
Under the combined effect of genetic growth and the fetus's movements against the walls of the uterus, the friction ridges become permanently set.
Source: Library of Congress — Fetal Fingerprint Formation · Checked on October 24, 2026
These muscles power every voluntary movement, from walking to facial expressions.
On their own, they make up about 40% of total body weight in a physically fit adult.
Source: Cleveland Clinic — Muscular System · Checked on October 24, 2026
The tongue only recognizes a few basic tastes; most of what we call the taste of a food, its aromas, actually comes from smell.
Molecules released by food travel up behind the throat to the nose: this is retronasal smell. That is why everything seems bland with a cold, while sweet, salty or bitter are still well perceived.
Source: Scientific American — Savory Science: Jelly Bean Taste Test · Checked on October 24, 2026
The 2014 study that put it forward has been criticized. Nobody really knows how many we can tell apart.
Our nose has about 400 types of receptors, which combine to recognize a very large number of odors.
Source: National Institutes of Health — Olfactory Range · Checked on October 24, 2026
MRI scans published in 2000 show that the posterior part of the hippocampus is larger in them, and the more so the longer their career.
To be licensed, they spend years learning about 25,000 London streets. The adult brain therefore remains moldable. A study by the same team in 2011 saw this area grow in trainees who passed the exam.
Source: PNAS (Maguire et al., 2000) · Checked on October 24, 2026
Oxygen-poor blood is dark red; it is the light passing through the skin that gives veins their bluish tint.
Oxygen-rich blood (in the arteries) is bright red, while blood returning to the heart is dark red. The blue you see under the skin comes from the way light is absorbed and scattered by tissues. During a blood draw, the blood that comes out is indeed red.
Source: Science ABC — If blood is red, why do veins look blue? · Checked on October 24, 2026
Around the eyes, skin is about 0.5 mm (0.02 in) thick, compared with several millimeters on the palms and the soles of the feet.
This thinness explains why dark circles and the first wrinkles appear early there: the small blood vessels show more clearly through the skin, and it contains very little fat.
Source: PubMed — Skin thickness of Korean adults · Checked on October 24, 2026
Without gravity, muscles and bones weaken: daily exercise helps limit muscle loss and bone loss in orbit.
This training also helps them stay fit for the return to Earth, where they have to bear their own weight again. It limits the loss without always eliminating it completely: space agencies are trying to improve these exercise programs.
Source: NASA (blog de la Station spatiale) · Checked on October 26, 2026
The two hands together have 54 bones, more than a quarter of the 206 bones in an adult.
This abundance of jointed bones explains the precision of our movements. The 14 bones of the fingers and thumb (phalanges) are the ones that move most finely.
Source: InformedHealth.org (IQWiG) — Bones and joints · Checked on October 26, 2026
This system is called the glymphatic system.
During deep sleep, spaces open up between brain cells, letting fluid flow through and carry the waste away.
Source: National Institutes of Health — Glymphatic System · Checked on October 24, 2026
The intestinal villi multiply the surface available to absorb nutrients into the blood.
Thanks to its folds, villi and microvilli, the small intestine unfolds about 30 square meters (about 320 square feet) of surface, not the 250 square meters of a tennis court once claimed in textbooks (a 2014 estimate).
Source: Helander & Fändriks — Surface area of the digestive tract revisited (Scand. J. Gastroenterol., 2014) · Checked on October 24, 2026
This pea-sized gland regulates sleep by secreting melatonin mostly at night, when the light dims.
Descartes chose it because it is a single structure located at the center of the brain, whereas most structures come in pairs. We now know that it mainly serves to signal nighttime to the rest of the body.
Source: Encyclopædia Universalis — Épiphyse ou glande pinéale · Checked on October 24, 2026
The ulnar nerve passes almost under the skin, behind the elbow, protected by very little tissue.
The impact compresses it and sends shocks toward the little finger and ring finger, hence the feeling of electricity. The name “funny bone” is a pun often explained by the resemblance to “humerus,” the arm bone.
Source: McGill Office for Science and Society — The funny bone is not a bone · Checked on October 24, 2026
After his moonwalk in December 1972, Harrison Schmitt sneezed, with red eyes and a scratchy throat, and spoke of “lunar hay fever.”
The symptoms lasted about two hours. A NASA doctor saw it as an allergic reaction to lunar dust. That didn't stop Schmitt from bringing back more rock samples than on any other Apollo mission.
Source: Mental Floss · Checked on October 26, 2026
They are among the rare nerve cells that regenerate.
Unlike cells in the eye or inner ear, the olfactory neurons in the nose keep growing back to replace damaged ones.
Source: National Institutes of Health — Olfactory Neurons Regeneration · Checked on October 24, 2026
The brain then eliminates little-used synapses, a “pruning” that continues until adolescence.
The peak arrives at different ages depending on the brain region, and the excess reaches about 50% compared with an adult. Connections that are used get stronger, the others disappear. Having more connections does not mean being smarter: it is this pruning that makes the brain efficient.
Source: Neuropsychopharmacology — Normal Development of Brain Circuits · Checked on October 24, 2026
The flexibility of this muscular organ lets it take in big meals without bursting.
Empty, the stomach is about the size of a closed fist, but its folded inner walls (the rugae) unfold widely to adapt to big feasts.
Source: Cleveland Clinic — Stomach Capacity · Checked on October 24, 2026
As soon as two tasks demand attention, each switch from one to the other costs time and increases errors.
Walking while listening to music is possible because one of the two tasks is automatic. Writing a message while driving, on the other hand, pits two tasks that require thought against each other: that is why multitasking is a myth for demanding tasks.
Source: Wake Forest University — The 'switch cost' of multitasking · Checked on October 24, 2026
Randy Gardner, 17, stayed awake for 264 hours; his first recovery sleep lasted about 14 hours.
Stanford researchers monitored him: problems with mood, concentration and memory, along with mild hallucinations. Guinness World Records no longer lists this kind of record, considered dangerous. Do not try it.
Source: BBC — The boy who stayed awake for 11 days · Checked on October 24, 2026
Its pH is around 1.5 to 3, which is also what destroys most of the microbes you swallow.
The stomach wall protects itself with a layer of mucus that it constantly renews.
Source: Cleveland Clinic — Stomach Acid Strength · Checked on October 24, 2026
Older calculations said 10 times more; recent measurements give a ratio close to 1 to 1.
These bacteria weigh about 200 grams (7 oz) in total, according to recent estimates.
Source: National Institutes of Health — Human Microbiome Project · Checked on October 24, 2026
It's a myth: the head accounts for about 7 to 10% of heat loss.
The myth comes from American military experiments in the 1950s, in which volunteers wore a suit but kept their heads bare. If your head feels cold, it's because it is very sensitive and often the only part exposed. Example: a hat protects you no more than a pair of gloves.
Source: Library of Congress — Heat Loss from Head · Checked on October 24, 2026
Even the mineral structure of the skeleton holds moisture inside.
This water built into the bone matrix gives bones their flexibility and elastic strength so they don't break too easily.
Source: National Institutes of Health — Bone Composition · Checked on October 24, 2026
This intense sleep phase corresponds to the times when the brain dreams most vividly.
Brain activity during REM sleep is very close to that of wakefulness, while the body's muscles are completely paralyzed to prevent movement.
Source: National Sleep Foundation — REM Sleep · Checked on October 24, 2026
Pain receptors in the palate send the signal through the trigeminal nerve, and the brain places it at the forehead. The pain lasts from 20 seconds to 2 minutes.
Eating fast raises the risk: 27% of people who swallowed ice cream in under 5 seconds had pain, versus 12% of those who took more than 30 seconds. Pressing your tongue against the roof of your mouth is often recommended, with no solid proof.
Source: Harvard Health — What causes brain freeze? · Checked on October 26, 2026
Where the optic nerve leaves the retina, there are no light-sensitive cells: that part of the visual field is invisible.
The brain fills in the hole using the other eye and the surrounding details. You can reveal it with a simple test: a cross and a dot drawn on a sheet of paper, one eye closed, and the dot disappears at a certain distance.
Source: Scholarpedia — The Blind Spot · Checked on October 24, 2026
These “otoacoustic emissions” were first recorded in 1978 by Britain’s David Kemp.
The cochlea actively amplifies sounds, and a small echo comes back out, which a microphone can pick up in the ear canal. In the maternity ward, this quick, painless test helps detect deafness in the first days of life.
Source: Canadian Audiologist — The Biggest Paradox in Audiology · Checked on October 24, 2026
The exceptional elasticity of this muscular organ shelters the growing fetus.
Going from the size of a small pear to that of a watermelon, the uterus returns to its original size just a few weeks after childbirth.
Source: American College of Obstetricians and Gynecologists · Checked on October 24, 2026
This enteric nervous system lines the digestive tract; it is estimated to have about 500 million neurons, several times more than the spinal cord.
It controls the contractions of digestion largely on its own, hence its nickname “second brain.” It doesn’t think, though: it constantly exchanges signals with the brain through the vagus nerve and through hormones.
Source: Cleveland Clinic — The Gut-Brain Connection · Checked on October 24, 2026
Arthur Fox, a chemist at DuPont, released a cloud of PTC powder: his colleague found it bitter, he tasted nothing.
The difference is genetic, tied to a bitter-taste receptor gene. Depending on the population, about one person in four cannot perceive the bitterness of PTC. This may influence tastes for certain bitter vegetables such as cabbage.
Source: faculty.washington.edu — Scientists Find Bitter Taste Gene · Checked on October 24, 2026
Frequency varies by study, from 1 birth in 700 to 1 in 30,000, according to the medical literature.
These teeth are often poorly anchored: they can interfere with breastfeeding, and a dentist sometimes decides to remove them. They are called “natal” teeth if present at birth and “neonatal” teeth if they come in during the first month.
Source: PMC — Natal teeth: a review · Checked on October 26, 2026
Kupffer cells, which sit in the liver's blood vessels, make up 80 to 90% of the macrophages found in all the body's tissues.
The liver filters blood coming from the intestine: macrophages there capture bacteria and debris before they circulate everywhere. They also play a role in liver diseases.
Source: PubMed Central (étude ALK1, Kupffer cells) · Checked on October 26, 2026
A sound coming from the side reaches the nearer ear at most 0.6 millisecond sooner; we can detect differences of 10 microseconds.
10 microseconds correspond to a sound travel distance of about 3 millimeters (0.12 in). The brain combines these delays with differences in volume between the two ears. With only one ear, locating a noise becomes much harder.
Source: Frontiers in Psychology — Auditory localization: a comprehensive practical review · Checked on October 24, 2026
That's nearly 30,000 liters (about 8,000 gallons) in a lifetime: enough to fill a small backyard pool.
Saliva moistens food, starts the digestion of starch and protects teeth from bacteria. You swallow most of it without even thinking about it, day and night.
Source: Library of Congress — Saliva Production · Checked on October 24, 2026
In 1987, Robert Provine had volunteers breathe air rich in oxygen or in CO2: their yawning rate did not change.
The most studied hypothesis today is that yawning may help cool the brain, but this is still debated. The exact role of yawning has not been settled by science.
Source: University of Washington — Yawning.. and why yawning is contagious · Checked on October 24, 2026
A sneeze briefly changes the pressure in the chest and the heart rate may vary for a moment, but the heart keeps beating.
People also say you cannot sneeze with your eyes open: we close them by reflex, but nothing forces us to. Both myths are passed down from generation to generation with no medical basis.
Source: Healthline — Does Your Heart Stop When You Sneeze? · Checked on October 24, 2026
The chemical elements that make up our body are found everywhere in nature.
Besides carbon, our body holds enough iron to make a large nail, and enough phosphorus to make plenty of match heads.
Source: Library of Congress — Chemical Elements of the Human Body · Checked on October 24, 2026
This residual volume, 1 to 1.5 liters (1 to 1.6 quarts) in adults, keeps the lungs from emptying completely like a balloon.
It helps keep the air sacs open between breaths. At rest, you move only about half a liter (about 1 pint) of air with each breath, while total lung capacity reaches about 6 liters (about 6.3 quarts).
Source: StatPearls (NCBI Bookshelf) — Physiology, Residual Volume · Checked on October 24, 2026
The vascular network is a gigantic microscopic maze spread throughout the body.
Adding up arteries, veins and capillaries, a single human body holds more than 100,000 kilometers (62,000 miles) of biological tubing.
Source: National Institutes of Health — Blood Vessel Length · Checked on October 24, 2026
The soles of the feet are among the areas of the body richest in sweat glands.
By common estimates, the feet can produce up to a quarter of a liter (about half a pint) of sweat a day, which is why shoe hygiene matters so much, and why feet can end up smelling.
Source: American Podiatric Medical Association — Sweaty Feet · Checked on October 24, 2026
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