You live inside one of the most amazing machines ever studied. Your body builds new skin, keeps your heart beating without being told and swaps out its own stomach lining every few days, all while you're busy doing other things. The 50 facts below are based on well-established science and are meant just for fun and curiosity.
Once you've read them all, see how much you remember with our science trivia quiz. Or compare your amazing body with some of nature's oddest designs on our animal fun facts page.
Bones and Muscles
- Babies have more bones than adults. A newborn starts with nearly 300 bones and cartilage pieces. Many of them fuse together while a child grows, leaving a typical adult with 206.
- Your smallest bone is about the size of a grain of rice. The stirrup bone, or stapes, sits deep inside your ear and helps pass sound vibrations along to your inner ear.
- Your hands and feet hold more than half of your bones. Each hand has 27 bones and each foot has 26, which is what makes fingers and toes so flexible.
- Your thigh bone is your longest and strongest bone. The femur runs from your hip to your knee and supports much of your weight when you stand, walk and jump.
- One bone in your body isn't connected to any other bone. The horseshoe-shaped hyoid bone in your neck is held in place by muscles and ligaments, and it helps you swallow and speak.
- Muscles can only pull, never push. That's why they work in teams. When your biceps tightens to bend your arm, your triceps tightens to straighten it again.
- Your biggest muscle is the one you sit on. The gluteus maximus helps you stand up, climb stairs and keep your body upright.
- You're a little taller in the morning. During the day, the soft discs between your spine bones get slightly squashed. They spread out again while you sleep, so you wake up around a centimeter taller.
Brain and Nerves
- Your brain is an energy hog. It makes up only about 2% of your body weight but uses roughly 20% of your body's energy.
- Your brain has about 86 billion nerve cells. These cells, called neurons, constantly send signals to each other through trillions of connections.
- The brain itself can't feel pain. It has no pain sensors of its own. Headaches come from the nerves, muscles and blood vessels around the brain, not from the brain tissue.
- Some nerve signals travel faster than a high-speed train. The fastest signals zip along at about 120 meters per second, which is more than 400 km/h.
- You can't tickle yourself. Your brain predicts exactly how your own fingers will move, so it turns down the surprise that makes tickling feel ticklish.
- Your brain is wrinkly for a good reason. All those folds pack a large thinking surface into a small space, the way crumpling a sheet of paper lets it fit into your fist.
- Yawns are contagious. Seeing, hearing or even reading about someone yawning can make you yawn too. Scientists are still studying exactly why.
- Brain freeze starts in the roof of your mouth. When something icy touches your palate, blood vessels there quickly change size, and nerves send a signal that your brain feels as a sudden ache in your forehead.
Heart, Blood and Lungs
- Your heart beats about 100,000 times a day. That adds up to billions of beats over a lifetime, all without you ever having to think about it.
- Your heart is roughly the size of your fist. It sits in the middle of your chest, tilted slightly to the left.
- Your heart has its own built-in spark plug. A small cluster of special cells called the sinoatrial node sends out tiny electrical signals that set the rhythm of every heartbeat.
- The "lub-dub" sound is your heart's doors closing. Each beat's two sounds come from valves inside the heart snapping shut to keep blood flowing in the right direction.
- Red blood cells don't have a nucleus. Skipping the nucleus leaves more room to carry oxygen. Each red blood cell lasts about four months before it's replaced.
- Your blood makes a full trip around your body in about a minute. When you're resting, your heart pumps roughly your entire blood supply every minute or so.
- Your left lung is smaller than your right. The left lung has two sections instead of three, which leaves room for your heart.
- Your lungs are packed with hundreds of millions of tiny air sacs. These sacs, called alveoli, are where oxygen passes into your blood. Spread out flat, their surface would cover the floor of a small apartment.
- The "hic" in a hiccup is your vocal cords snapping shut. A hiccup begins with a sudden twitch of the diaphragm, the muscle under your lungs, which makes you gulp air just as your vocal cords close.
Super Senses
- Much of what you call taste is really smell. Your tongue senses only a few basic tastes, such as sweet, salty, sour, bitter and savoury. Your nose adds the rest, which is why food seems bland when you have a stuffy nose.
- Your nose has about 400 kinds of smell detectors. Different smells switch on different combinations of these receptors, letting you tell apart a huge variety of scents.
- Your taste buds are constantly being replaced. Taste cells only last about one to two weeks before new ones take their place.
- Your eyes see the world upside down. The lens in each eye flips the image it projects onto the back of your eye, and your brain turns it right side up.
- Each eye has a blind spot. There are no light sensors where the optic nerve leaves the eye, but your brain cleverly fills in the gap, so you never notice.
- The clear front of your eye gets oxygen straight from the air. The cornea has no blood vessels, which helps keep it perfectly see-through.
- Your inner ears help you balance. Tiny loops filled with fluid sense when your head moves. After you spin, the fluid keeps swirling for a moment, which is why the room seems to keep spinning.
- Your smallest muscle is inside your ear. The stapedius muscle is just a millimeter or two long, and it helps steady your tiniest bone when sounds get loud.
- You blink more than 10,000 times a day. Each blink spreads a fresh layer of tears across your eyes to keep them clean and moist.
Skin, Hair and Nails
- Your skin is your largest organ. It protects you from germs, helps control your temperature and lets you feel touch, heat and cold.
- Your outer skin is always being renewed. You shed tiny flakes of skin all day long, and the top layer is replaced about every month.
- Your hair and nails are made of the same stuff as a rhino's horn. They're all built from a tough protein called keratin, which is also found in hooves, claws and feathers.
- Fingernails grow faster than toenails. Nobody knows the full reason, but it may be linked to fingers being more active and having better blood flow.
- Goosebumps are a leftover from furrier ancestors. Tiny muscles pull your hairs upright when you're cold or scared. On a furry animal, that fluffs up the coat for warmth or to look bigger.
- Your fingerprints formed before you were born. They take shape in the first few months of growth before birth, and even identical twins have different fingerprints.
- Wrinkly bath fingers are controlled by your nerves. Your fingertips wrinkle in water because blood vessels under the skin narrow. Some scientists think the wrinkles may help you grip wet objects.
- The hair on your head grows about a centimeter a month. Each strand grows from its own follicle, and a scalp has roughly 100,000 of them.
Body Oddities
- Your stomach lining replaces itself every few days. Your stomach makes strong acid to break down food, so its inner surface is constantly renewed and coated in protective mucus.
- A growling stomach doesn't always mean you're hungry. The rumbling comes from muscles squeezing food, liquid and gas through your gut, and it can happen at any time. It's just louder when your stomach is empty.
- The DNA in one cell would stretch about two meters. Your body tightly coils that long thread so it fits inside a nucleus far too small to see without a microscope.
- You are made of tens of trillions of cells. They come in hundreds of types, from long, thin nerve cells to round, flexible red blood cells.
- Tooth enamel is the hardest substance in your body. It's even harder than bone, which helps your teeth crush and grind food for many years.
- Humans are the only living animals with true chins. Scientists still debate why our jaws grew this way, since even our closest animal relatives don't have them.
- Your body gives off about as much heat as a light bulb. At rest, an adult makes roughly 80 to 100 watts of heat, which is why a room full of people warms up quickly.
- Your liver can regrow. If part of a healthy liver is removed, the rest can grow back to close to its original size in a matter of weeks.
Myths we left out
These body "facts" are everywhere, but science says otherwise: - Myth: We only use 10% of our brains. Reality: Brain scans show activity throughout the brain, and even simple tasks use many different areas. - Myth: Your blood is blue inside your veins. Reality: Blood is always red. Veins only look blue because of the way light passes through skin. - Myth: Different parts of your tongue detect different tastes. Reality: Taste buds all over the tongue can sense every basic taste. - Myth: You lose most of your body heat through your head. Reality: Your head loses heat at about the same rate as any other uncovered part of your body. - Myth: Humans have only five senses. Reality: You also have senses for balance, temperature and knowing where your body parts are without looking.
Frequently asked questions
How many bones are in the human body?
A typical adult has 206 bones. Babies start with more, but many fuse together during childhood.
What is the largest organ in the human body?
The skin is the largest organ. Inside the body, the liver is the largest solid organ.
Is this page medical advice?
No. These facts are for fun and learning only. If you have a question about your own health, talk to a doctor, nurse or pharmacist.
Where can I find more fun facts and trivia?
Explore the stars with our space fun facts, or test yourself on any subject on our trivia quizzes page. Need something quick? Hit the bored button.