BioFacting

Human Facts

Fun facts about the human body and mind

A brain freeze starts 10 seconds after you eat the food
Human Fun Fact #32

A brain freeze starts 10 seconds after you eat the food

A brain freeze is your body's reaction to eating very cold foods. It is scientifically referred to as phenopalatine ganglioneuralgia. Your brain and body regulate temperature so when something cold is put into your mouth, your body wants to warm itself back up. The blood vessels in the mouth expand to push blood that will warm it up. Blood vessels in the brain also grow and shrink, and this causes the stabbing pain felt in the front and sides of the brain.

Babies rarely shed real tears in the first two weeks of life
Human Fun Fact #31

Babies rarely shed real tears in the first two weeks of life

Visible tears are not shed because the lacrimal glands, or tear glands, are still developing. This often takes anywhere from 2 weeks to 2 months to fully develop. Babies are still able to keep their eyes moist and healthy because the tears glands will produce just enough liquid for this process, but won't overflow.

The brain can identify images in as little as 13 milliseconds
Human Fun Fact #30

The brain can identify images in as little as 13 milliseconds

A team of neuroscientists from MIT has found that the human brain can process entire images that the eye sees for as little as 13 milliseconds. Previous studies suggested about 100 milliseconds, so this shows our extremely rapid processing speed. The eyes move about 3 times per second, both to get information to the brain and to move onto what we should look at next. This calibration allows for the rapid-fire processing seen when determining what an image is meant to be.

Your bones stop growing in length after you hit puberty
Human Fun Fact #29

Your bones stop growing in length after you hit puberty

This is due to growth cartilage. Growth cartilage, or growth plates, are areas at the end of long bones where new bone cells form, making them longer. As kids grow, the growth plates start hardening into solid bone and it becomes closed. Growth plates normally close toward the end of puberty, which will be about 13-15 for girls and 15-17 for boys.

You die faster without sleep than starvation
Human Fun Fact #28

You die faster without sleep than starvation

While a lack of sleep won't directly kill you, it especially deteriorates your mental health. A lack of sleep has been linked to lower alertness, poor concentration, and difficulty performing tasks that require logical reasoning. It also affects overall mood and energy. Starvation is a gradual process of the body breaking down proteins from the muscle to generate energy. Since this process is slower, the negative effects from a lack of sleep and issues such as a heart attack or stroke will occur first.

Dead skin cells decrease air pollution
Human Fun Fact #27

Dead skin cells decrease air pollution

People shed skin cells at a rate of 500 million cells per day. Studies have revealed that shed skin helps clean up indoor ozone levels. The oil in these skin cells, made up of cholesterol and squalene, are major contributors to dust. Squalene is a natural lipid and has specifically been shown to reduce indoor ozone levels roughly 2 to 15 percent.

Humans are the only known animal to blush
Human Fun Fact #26

Humans are the only known animal to blush

Blushing is a unique human expression caused by an involuntary response where the blood vessels in the facial skin dilate during times of embarrassment. This may be because embarrassment is a highly complex emotion, as it requires you to know what the other person is thinking about you. Other animals that have red faces like the uakari monkey use it as as a signal of physiological health.

Fingernails grow quicker than toenails
Human Fun Fact #25

Fingernails grow quicker than toenails

Fingernails grow faster mainly because of better blood circulation and more frequent stimulation from daily use. A popular theory is called "terminal trauma" which is where the body assumes that the fingernails are being worn down by the constant use of your fingers. Therefore, it makes up for this use with faster growth.

The gut has its own nervous system
Human Fun Fact #24

The gut has its own nervous system

Your gut has its own brain that controls sensations referred to as the enteric nervous system. It is two thin layers of more than 100 million nerve cells lining the gastrointestinal tract spanning from the esophagus to the rectum. This system is another division of the autonomic nervous system which governs automatic functions of internal organs. This "second brain" explains "gut feelings," and the sensation of butterflies in your stomach.

The cornea does not get oxygen from our blood
Human Fun Fact #23

The cornea does not get oxygen from our blood

Normally, oxygen is transported throughout the body by the blood. However, it would be dangerous for blood to be at the front part of the eyes. The liquid blocking the front part of the eyes would also cover our light source and cause blindness. Since the cornea is directly in contact with the air, it is able to efficiently get oxygen this way.

The largest artery of the human body is the aorta
Human Fun Fact #22

The largest artery of the human body is the aorta

The aorta delivers oxygen-rich blood from the heart to the circulatory system. It's more than a foot long and an inch in diameter at its widest point. It originates from the left ventricle of the heart and passes through the chest and abdomen, ending at your pelvis. Blood vessels branch off the aorta, extending its reach to muscles, nerves, and organs throughout the body.

We mainly breathe out of one nostril
Human Fun Fact #21

We mainly breathe out of one nostril

The split between the nostrils is about 75-25 when it comes to breathing. We have a "dominant" nostril that switches throughout the day. This is referred to as the nasal cycle. One nostril will become more congested, therefore contributing less to airflow, with this switching about every 2 hours.

Chainsaws were first invented for childbirth
Human Fun Fact #20

Chainsaws were first invented for childbirth

In the late 18th century, 2 Scottish doctors, John Aitken and James Jeffray, created a prototype of the chainsaw. It was first created for symphysiotomy, a surgical procedure that got rid of the pelvic bone to widen the pelvic outlet, and to remove diseased bone. At the time, it was seen as safer than a caesarian section since they were highly dangerous from a high risk of infection for both the mother and the child.

The Sun makes noises that we are unable to hear
Human Fun Fact #19

The Sun makes noises that we are unable to hear

Solar physicists were able to record acoustical pressure waves coming from the Sun. The Sun is able to make noise due to its constant flow of hot material on the surface followed by the sinking of cooled material toward the center. This noise is estimated to be extremely loud and sounds like screaming. However, the sound waves are normally at frequencies too low for the human ear to hear.

The brain eats itself
Human Fun Fact #18

The brain eats itself

The brain constantly changes its microstructure by "eating" itself. This process is referred to as phagocytosis, meaning "to devour" in Greek. In the brain, it is performed by a cell called microglia, which can "eat" neurons or the gaps between neurons called synapses. The purpose of this cleanup is to shape the neural circuits of the brain, removing unused connections that waste space or to prevent infection.

The liver is capable of rapid regeneration
Human Fun Fact #17

The liver is capable of rapid regeneration

The liver performs hundreds of functions like filtering toxins, regulating body temperature, and creating proteins. When a portion of the liver is removed, the liver's cells are able to divide and regrow the lost tissues in days. Medically, this makes donating a portion of the liver an easier process with a fast recovery time.

There are more bacterial cells than human cells in the body
Human Fun Fact #16

There are more bacterial cells than human cells in the body

While it was originally thought that there are 10 times more bacterial cells compared to human cells, the real number is closer to 1.3 times more. The average number of bacteria in the body ranges from around 30 trillion to 50 trillion. They take up a lot less space than human cells, and are either harmless or helpful. They play especially large roles in digestion and immune system development to aid the body.

Our ears and nose look like they never stop growing
Human Fun Fact #15

Our ears and nose look like they never stop growing

While the ears and nose change as we age, it is a myth that they continue to grow indefinitely. The ears and nose are mainly made of cartilage. Cartilage is made of fibers that begin to break down over time, causing it to weaken and become softer. Gravity causes the skin to sag which makes the nose and ears appear bigger.

Each person has a unique tongue print
Human Fun Fact #14

Each person has a unique tongue print

Just like fingerprints, humans have unique tongue prints too. The patterns of ridges, grooves, and small bumps on the surface of the tongue called papillae all contribute to this individuality. Tongue prints may prove to better in forensics since they are less exposed compared to fingerprints.

Human eyes can interpret about 10 million different colors
Human Fun Fact #13

Human eyes can interpret about 10 million different colors

The human eye can distinguish three colors - red, green, and blue. The retina has two types of photoreceptor cells, rods and cones. Rods detect the presence of light while cones detect different wavelengths of light, allowing the brain to interpret color. The three types of cones in the eye sense either red, green, or blue. These cones respond when they see their respective color of light. The signals then go to the brain, and the brain interprets the color based on which cells responded. The intensity of how the cones respond allows for different shades of the color, which is how we can see millions of colors.

Humans can smell rain better than sharks can smell blood
Human Fun Fact #12

Humans can smell rain better than sharks can smell blood

While it isn't the rain itself that humans smell, we are capable of smelling geosmin, a chemical released by dead microbes, at a level of 5 parts per trillion. The moistening of the soil from rain speeds up the breaking down of dead or decaying matter by bacteria. Many people's favorite smell is the air after a storm because it's so distinct. The scent was termed "petrichor" from Greek "petros" (stone) and "ichor," or the blood of the gods. A shark is capable of smelling blood at one part per million. This means that human noses are over 200,000 times more sensitive to geosmin.

About 60% of the human body is made up of water
Human Fun Fact #11

About 60% of the human body is made up of water

Water serves several essential functions that cause us to have so much of it in the body. It is a vital nutrient to the life of every cell, causes us to sweat and respire which regulates our body temperature, transports carbohydrates and proteins through the bloodstream, helps with waste disposal, forms saliva, and lubricates the joints. This 60% value may vary based on the distribution of body fat and tissue, as there is more water in lean muscle compared to fatty tissue.

The distance of all your blood vessels would wrap around the Earth twice
Human Fun Fact #10

The distance of all your blood vessels would wrap around the Earth twice

The network of blood vessels lain out from end to end would stretch for about 60,000 miles. The Earth's circumference is about 25,000 miles. So, they would be able to stretch around the Earth over two times. The capillaries, the smallest blood vessels in the body, would make up about 80% of this length.

The brain cannot feel pain
Human Fun Fact #9

The brain cannot feel pain

Sensory nerve fibers known as nociceptors are responsible for stimulating pain signals that are perceived by the brain. However, the brain itself doesn't feel pain because it lacks nociceptors in the brain tissue.

The most vivid dreams happen during REM sleep
Human Fun Fact #8

The most vivid dreams happen during REM sleep

Rapid eye movement (REM) sleep is the final of 4 stages in the sleep cycle. During this sleep, brain activity picks up and is similar to the level of brain activity when awake. At the same time, the body experiences atonia, also known as muscle paralysis. Only the muscles that control breathing and the eyes are active. As the night goes on, the REM stages get longer and the high brain activity allows for vivid dreams.

Stomach acid is so strong that it can even dissolve metal
Human Fun Fact #7

Stomach acid is so strong that it can even dissolve metal

The pH scale measures acidity versus alkalinity which ranges from 0 to 14, with 0 being the most acidic. Stomach acid has a pH between 1 and 2, making it very acidic. The stomach's low pH level is mostly due to hydrochloric acid in stomach acid. The main reason for this acidity is to help digest food and absorb nutrients. Mucus protects the lining of the stomach from the acid so that it doesn't damage your stomach.

We are about 1 centimeter taller in the morning
Human Fun Fact #6

We are about 1 centimeter taller in the morning

This slight change happens due to gravity. During the day, gravity compresses the cartilage in your spine, causing you to "shrink" a little. When lying down in a resting position at night, the spine "spreads out" or decompresses a little so when you wake up in the morning you are slightly taller.

All the neurons in the brain generate enough electricity to power a small lightbulb
Human Fun Fact #5

All the neurons in the brain generate enough electricity to power a small lightbulb

The brain contains about 86 billion neurons that send chemical and electrical signals throughout the brain in an intricate network to help us understand the world around us. A single neuron generates only a tiny amount of electricity but all together your neurons generate about 20 watts of power, which is enough to power a lightbulb.

Humans glow in visible light
Human Fun Fact #4

Humans glow in visible light

The human body emits visible light that is 1,000 times less intense than our naked eyes are sensitive to. A study conducted by Japanese scientists found that the light emitted rises and falls with the day. It was also found that our faces glow more than the rest of the body. This could be because the face gets the most exposure to sunlight. Melanin, the pigment behind skin color, has fluorescent components which could increase the body's light production.

Yawns are actually contagious.
Human Fun Fact #3

Yawns are actually contagious.

This is related to the phenomenon called social mirroring. It is where organisms imitate the actions of others, and several behaviors can fall into this category. This behavior can also be linked to mirror neurons in the brain, although they are a controversial topic among scientists regarding whether they function in the same way as they do in monkeys. These neurons are said to be involved in matching what we sense and feel to the way we move, which links back to empathy. Mirror neurons respond equally when performing an action or witnessing someone else do that same action.

Babies are born with around 300 bones.
Human Fun Fact #2

Babies are born with around 300 bones.

Babies are born with more than the normal 206 bones in adulthood because these bones are constantly growing and changing shape as the baby develops. As the baby grows, some of the bones will start fusing together to eventually form the 206 bones. The skeletal structure starts out as cartilage, which is a firm tissue that is softer and more flexible than bone, allowing for this fusion to occur. The cartilage will eventually turn to hard bone as more calcium is absorbed.

Your pupils expand when you see someone you love.
Human Fun Fact #1

Your pupils expand when you see someone you love.

This is due to the fact that when a person feels positive emotions, it is often aligned with dopamine and serotonin release in the brain. The iris, the colored part of the eye that surrounds the pupil, is a muscle and part of its job is to control the size of the pupil by dilating and constricting in order to regulate how much light enters the eye. The chemical release of dopamine has been shown to cause the pupils to dilate, which is why looking at someone you love causes your pupils to dilate.