The outer layer of skin constantly renews itself. Dead cells flake off and are a major component of household dust.
Wacky Facts
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Fingerprints form in the womb and never change.
Fingerprint ridges form by around the 17th week of pregnancy. Even identical twins have different fingerprints.
Humans share about 60% of their genes with bananas — but not how you think.
About 60% of human genes have a recognisable counterpart in the banana genome, reflecting basic cell functions shared by all life. It does not mean we are 60% banana.
Goosebumps are left over from furry ancestors.
Tiny muscles raise body hair to trap warmth or look bigger — useful for furry animals, not much for us.
Bones are stronger than steel of the same weight.
Weight for weight, bone is remarkably strong, especially under compression, because of its mix of collagen and mineral.
Your liver can regrow.
The liver can regenerate to its full size even after a large part is removed, which makes living-donor transplants possible.
Your stomach gets a new lining every few days.
The cells lining the stomach are replaced frequently so its strong acid does not digest the stomach itself.
The smallest bone in your body is in your ear.
The stapes, or stirrup bone, is about 3 mm long and helps carry sound to the inner ear.
Muscles cannot push, only pull.
Every movement comes from muscles contracting; opposite muscle pairs move a joint back again.
The brain uses about 20% of the body’s energy.
Although it is only around 2% of body weight, the brain consumes roughly a fifth of the body’s energy at rest.
Your nose and ears keep growing slowly throughout life.
Cartilage changes and gravity make noses and ears appear to grow with age.
A human sneeze reflex can be triggered by sunlight.
About 18–35% of people sneeze when suddenly exposed to bright light.
Adults have fewer taste buds than children.
Taste buds are replaced every one to two weeks, but their number declines with age.
Your eyes stay the same size from birth — nearly.
Eyes grow from about 16–17 mm at birth to about 24 mm in adults, much less than the rest of the body.
Stomach acid is strong enough to dissolve some metals.
Gastric acid has a pH of about 1.5–3.5. The stomach lining protects itself with mucus and constant cell renewal.
The cornea has no blood vessels.
It gets oxygen directly from the air and nutrients from tears and the fluid behind it.
Humans are the only animals known to blush.
Charles Darwin called blushing “the most peculiar and the most human of all expressions”.
Your heart beats about 100,000 times a day.
At about 70 beats a minute, that is over 2.5 billion beats in a lifetime.
Fingerprints form before birth.
Ridges develop in the womb around 10–16 weeks and remain the same throughout life; even identical twins differ.
Stomach rumbling has a name: borborygmi.
The noise comes from gas and fluid moving through the intestines, and it happens whether you are hungry or not.
The small intestine is about 6 metres long.
In adults the small intestine averages around 6–7 metres, folded into the abdomen. Most nutrient absorption happens there.
Your body replaces most of your red blood cells every few months.
Red blood cells live about 100–120 days. Your bone marrow makes millions of new ones every second to replace them.
Fingernails grow faster on your dominant hand.
Nails grow about 3 mm a month on average, faster in summer and on the hand you use most.
You blink around 15–20 times a minute.
Blinking spreads tears across the eye to keep it moist and clean. People blink much less when staring at screens, which can cause dry eyes.