Human Body Facts for Kids
Surprising facts about your body
Yawning is so contagious that even reading or thinking about yawning can make you do it. Research shows that chimpanzees, dogs, and other social animals also catch yawns from each other and even from humans. Scientists believe contagious yawning may be linked to empathy and social bonding.
Your two kidneys filter your entire blood supply about 30 times every day, cleaning out waste products and excess water. They produce about 1-2 liters of urine per day. Each kidney contains about one million tiny filtering units called nephrons.
Relative to its size, the masseter muscle in your jaw is the strongest muscle in the human body. It can close your teeth with a force of up to 200 pounds per square inch on your molars. Chewing is one of the most repeated muscular actions humans perform throughout their lives.
The average human hair grows about half an inch per month, or about six inches per year. Each hair follicle goes through cycles of growing, resting, and shedding. Humans lose about 50 to 100 hairs every day, which is completely normal.
The idea that people are either 'left-brained' (logical) or 'right-brained' (creative) is a popular myth. Brain imaging studies show that people use both sides of their brain for virtually all tasks. While some functions do have a slight preference for one side, creativity and logic are both distributed throughout both hemispheres.
The rumbling sound your stomach makes is called borborygmi (bor-bor-ig-mee). It's caused by gas and fluids being pushed through your intestines by muscular contractions called peristalsis. Your digestive system makes these sounds all the time, but they're louder when your stomach is empty because there's no food to muffle the sound.
Your body sheds and replaces the entire outer layer of skin roughly every 2 to 3 weeks. You lose about 30,000 to 40,000 dead skin cells every hour. Over a lifetime, the average person sheds about 105 pounds of skin.
Although the brain makes up only about 2% of your body weight, it consumes approximately 20% of all the oxygen and calories your body uses. The brain never truly rests — it is just as active during sleep as during waking hours, just doing different tasks. This enormous energy demand is why the brain is so vulnerable to disruptions in blood flow.
Goosebumps occur when tiny muscles at the base of each hair follicle contract, making the hair stand up. In our furry ancestors, this would have made them look bigger to predators and trap more insulating air when cold. Since humans don't have thick fur, our goosebumps serve no real practical purpose today.
About 55% of your blood is made of plasma, which is mostly water carrying proteins, hormones, and nutrients. The remaining 45% is made of red blood cells, white blood cells, and platelets. If you donate blood, your body replaces the plasma within a few days, though the red blood cells take about 4-6 weeks to fully recover.