Author: wahidbodelune

Fireflies and jellyfish glow. So, in a tiny way, do you. In 2009, scientists in Japan captured photographs of visible light coming from human skin. Nobody in the room could see it, but a special camera could.

The experiment

Researchers at the Tohoku Institute of Technology placed five healthy young men, one at a time, in a completely dark, light-sealed room. They sat bare-chested in front of an extremely sensitive camera, cooled to very low temperatures so it could detect single particles of light.

Each session lasted 20 minutes and was repeated every three hours from 10 am to 10 pm, over three days. The study was published in the journal PLoS ONE.

What they found

The human body really does give off a faint visible light. The glow was about 1,000 times weaker than what the naked eye can detect. It is not body heat: heat comes out as infrared light, which is a different thing.

The face glowed more than the rest of the body. And the glow followed a daily rhythm: it was weakest around 10 am and strongest around 4 pm, then fell again toward evening.

Where does the light come from?

Scientists think it is a side effect of metabolism. As cells use energy, they produce reactive molecules. When these react with fats and proteins, a tiny amount of energy can be released as light.

Keep it in proportion

The colourful pictures from the study use false colours to show brightness. They are not what a person would see, and the study was very small. This is not an “aura”. It is ordinary chemistry, measured with an extraordinary camera.

Sources

• Kobayashi et al. (2009), PLoS ONE: Imaging of ultraweak spontaneous photon emission from human body
• Live Science: Humans glow in visible light

This article is for curiosity and learning only and is not medical advice.

You cut them, they come back. But how fast, exactly? A careful study of healthy young adults measured it, and the gap between fingers and toes is bigger than most people think.

The numbers

In a 2010 study published in the Journal of the European Academy of Dermatology and Venereology, researchers asked young American adults to mark their nails and measure how far the mark moved over one to three months.

The result: fingernails grew an average of 3.47 mm per month, a little over a tenth of a millimetre per day. Toenails grew just 1.62 mm per month, less than half as fast.

Not all fingers are equal

Left and right hands grew at about the same speed. But the little fingernail grew more slowly than the other fingernails, and the big toenail grew faster than the other toenails.

Younger age, being male and nail biting all seemed linked to slightly faster growth, but those differences were not strong enough to be certain.

Faster than in the past?

The researchers noted that nail growth in their study was faster than in estimates made decades earlier. The reason is not known.

What it means in real life

At about 3.5 mm a month, a fingernail that is completely lost takes several months to grow back. A lost big toenail can take a year or more, which is why a bruise under a toenail seems to stay for so long.

Nails are made of keratin, the same tough protein found in hair. They grow from a hidden area under the skin at the base of the nail, called the matrix. Creams on the nail itself cannot speed that up.

Sources

• Yaemsiri et al. (2010), Growth rate of human fingernails and toenails in healthy American young adults (PubMed)
• Harvard BioNumbers: Average fingernail and toenail growth rate

This article is for curiosity and learning only and is not medical advice.

Hic! Everyone gets them, nobody asks for them, and they usually stop on their own. But why does the body do something so strange? For a long time there was no good answer. A study on newborn babies has given scientists a new idea.

What a hiccup actually is

Under your lungs sits a dome-shaped muscle called the diaphragm. It is the main muscle you use to breathe. During a hiccup, the diaphragm suddenly contracts on its own, pulling air in fast. A split second later, the opening between your vocal cords snaps shut. That quick stop of air is what makes the “hic” sound.

Hiccups start before birth

Hiccups are one of the earliest movements a baby makes. They begin in the womb at around 9 weeks of pregnancy. Babies born early hiccup a lot: an estimated 1% of their time, roughly 15 minutes a day.

The UCL study

In 2019, researchers at University College London recorded the brain activity of 13 newborn babies on a hospital ward, aged from 30 to 42 weeks of development. Small sensors on the babies’ bodies showed exactly when each hiccup happened.

Each hiccup triggered a clear response in the brain: two large brainwaves, followed by a third. The third wave looked similar to the brain’s reaction to a sound, which suggests the baby brain may be linking the “hic” with the feeling of the diaphragm moving.

The researchers think this may help a newborn’s brain learn how to sense and later control its breathing muscles. If that is right, adult hiccups could be a leftover reflex from a time when they had a real job to do.

What it does not tell us

The study was small and looked only at babies. It does not prove why adults hiccup, and it does not explain the many home remedies people swear by. Most hiccup bouts are harmless and go away by themselves.

Sources

• UCL News: Newborn baby hiccups could be key to brain development
• Whitehead et al. (2019), Clinical Neurophysiology

This article is for curiosity and learning only and is not medical advice.

You have probably heard that you are “mostly water”. It is true, but the full picture is more surprising. Some parts of you are almost as wet as a fruit, while others are much drier than you might expect.

The big number: about 60%

According to the U.S. Geological Survey, water makes up about 60% of an adult human body. The exact amount changes from person to person. It depends on age, sex and body type, and people with more fat tissue have a lower percentage of water, because fat holds less water than muscle.

Babies are the wettest of all. A newborn is roughly three quarters water, and the share slowly drops as we grow.

Organ by organ

Classic measurements reported by the USGS give these approximate numbers:

Lungs: about 83% water
Muscles and kidneys: about 79%
Brain and heart: about 73%
Skin: about 64%
Bones: about 31%

Yes, even your bones are nearly one third water. They feel hard and dry, but living bone is full of blood vessels and moist tissue.

Why your body needs so much

Water helps carry nutrients and oxygen to your cells, removes waste through your kidneys, cushions your joints, and lets you cool down through sweat. Almost every chemical reaction inside your cells happens in water.

Your body is also always losing water, through breathing, sweating and the toilet, so it has to be replaced every day through drinks and food.

Sources

• USGS Water Science School: The water in you, water and the human body

This article is for curiosity and learning only and is not medical advice.

Stay in the bath long enough and your fingertips turn into little prunes. Most people think the skin simply soaks up water and swells. The real answer is more interesting: your nervous system is doing it on purpose.

It is your nerves, not just the water

Doctors have known since the 1930s that fingers with damaged nerves do not wrinkle in water. That was the first clue. If wrinkling were only about skin soaking up water, nerves would not matter.

Today we know the wrinkles come from the autonomic nervous system, the automatic system that also controls your heartbeat, breathing and sweating. After a while in water, it makes the small blood vessels under the skin of your fingertips narrow. The soft tissue shrinks a little, and the skin on top folds into ridges.

The tyre tread idea

In 2011, scientists suggested that the ridges could work like the tread on a car tyre in the rain, giving water a path to drain away so the finger can grip better.

In 2013, a team at Newcastle University in the UK tested this. Twenty volunteers moved wet marbles and small weights from one container to another, once with normal fingers and once after soaking their hands in warm water for 30 minutes. With wrinkled fingers, they moved the wet objects about 12% faster. With dry objects, wrinkles made no difference.

So why are our fingers not always wrinkled?

The researchers were not sure. One idea is that permanent wrinkles could make fingertips less sensitive, or more likely to catch on things. Smooth when dry and ridged when wet may simply be the best of both worlds.

Scientists still debate how much the wrinkles really help, and later studies have not all agreed. But one thing is clear: pruney fingers are an active response from your body, not just wet skin.

Sources

• Kareklas et al. (2013), Biology Letters: Water-induced finger wrinkles improve handling of wet objects
• Scientific American: Why do our fingers and toes wrinkle during a bath?
• Science News: Pruney digits help people get a grip

This article is for curiosity and learning only and is not medical advice.

Every person on Earth yawns, every day. Many animals do it too. Yet scientists still do not fully agree on why. One of the most interesting answers is that a yawn helps cool your brain.

It is probably not about oxygen

A popular idea says we yawn to take in more oxygen. But when researchers changed the levels of oxygen and carbon dioxide that people breathed, yawning did not change in the way that idea predicts. So most scientists no longer think oxygen is the main reason.

The brain-cooling theory

Psychologist and biologist Andrew Gallup and his colleagues have studied yawning for years. Their idea is that a yawn works a bit like a radiator. The big stretch of the jaw and the deep breath of cooler air help bring cooler blood toward the brain and move warmer blood away.

Several findings fit this idea:

• In rats, brain temperature rose before a yawn and dropped after it.
• People held cold packs to their foreheads, or breathed only through their nose, and yawned less when watching videos of others yawning.
• People tend to yawn less when the air is hotter than the body, because breathing in warm air would not cool anything.

This could also explain why we often yawn when we are tired. Lack of sleep is linked to a warmer brain, and yawning is very common around bedtime and right after waking up.

Why yawns are contagious

You are more likely to yawn if you see, hear, or even read about someone else yawning. (Did you yawn just now?) Some research links contagious yawning to empathy and social bonds. Gallup has suggested it might once have helped groups stay alert together. Scientists are still testing these ideas.

The honest answer

Brain cooling is one of the best-supported theories, but there is no final answer yet. Other researchers think yawning mainly helps the brain switch between states, like sleeping and waking. It may well do more than one job.

Sources

• Science News: Latest research awakens debate over why we yawn
• The Naked Scientists: Why do we yawn? (interview with Gordon Gallup)

This article is for curiosity and learning only and is not medical advice. Very frequent yawning that is new or unusual for you is worth mentioning to a doctor.

While you read this sentence, your body has built millions of brand-new cells. It does this quietly, all day and all night. In 2021, two scientists finally worked out how fast it really happens.

330 billion cells a day

Ron Sender and Professor Ron Milo of the Weizmann Institute of Science in Israel combined decades of research on how long each type of cell lives. They published their results in the journal Nature Medicine.

Their estimate: an adult body has about 30 trillion human cells, and around 330 billion of them are replaced every day. That works out to nearly 4 million new cells every second.

Most of them are blood

The busiest factory is your blood. About 86% of the cells replaced each day are blood cells, mostly red blood cells and a type of white blood cell called neutrophils. Almost all of the rest are cells lining your gut, which are renewed every few days.

Because blood cells are so light, all this new tissue weighs surprisingly little: roughly 80 grams a day, about the weight of a couple of small eggs.

A “new you” in about 80 to 100 days

At this speed, your body makes a number of new cells equal to all the cells you have in roughly 80 to 100 days. Measured by weight instead of number, it takes much longer, because heavy cells like fat and muscle live for years.

The 7-year myth

You may have heard that every cell in your body is replaced every seven years. That is a myth. Some cells are replaced in days, while others stay with you for life. Most neurons in your brain and the cells in the lens of your eye are, for the most part, never replaced. So you are both new and the same at once.

Sources

• Sender & Milo (2021), Nature Medicine: The distribution of cellular turnover in the human body
• Weizmann Institute of Science: Cell replacement by the numbers
• Scientific American: Our bodies replace billions of cells every day

This article is for curiosity and learning only and is not medical advice.

A cold wind, a scary movie, a song that moves you, and suddenly tiny bumps rise all over your arms. Even Charles Darwin wondered why. For a long time, goosebumps were seen as a useless leftover. New research suggests they are part of something more clever.

What actually happens in your skin

Every hair on your body grows from a small pocket in the skin called a hair follicle. Attached to each follicle is a tiny muscle, the arrector pili. When your body senses cold or a strong emotion, your sympathetic nervous system (the “fight or flight” system) tells this muscle to contract.

The muscle pulls the hair upright and pulls in the skin around it. That little raised spot is a goosebump.

Why animals need it

For furry animals, raised hair traps a layer of air that helps keep them warm. It can also make an animal look bigger when it is scared, like a cat puffing up its tail. Humans have much less body hair, so for us the warming effect is tiny.

The Harvard discovery

In 2020, a team led by Professor Ya-Chieh Hsu at Harvard, working with Professor Sung-Jan Lin of National Taiwan University, published a study in the journal Cell. Looking at the skin of mice under very high magnification, they found that the nerve behind goosebumps does more than move the muscle. It also wraps around the stem cells that make new hair, like a ribbon.

In short cold spells, the nerve simply makes the muscle contract: goosebumps. But when the cold lasts longer, the nerve becomes more active and signals the stem cells to wake up and grow new hair. The muscle turned out to be essential: when it was removed, the nerve connection to the stem cells was lost.

As the researchers described it, goosebumps are a quick, short-term response, while the same system helps the body grow a warmer coat over the long term.

What it means for us

The study was done in mice, so scientists are careful about what it means for humans. But the same muscle-and-follicle connection exists across mammals, which suggests goosebumps may be less useless than they look. They are a small window into how our skin listens to the world around it.

Sources

• Harvard Stem Cell and Regenerative Biology: The real reason behind goosebumps
• Shwartz et al. (2020), Cell: Cell types promoting goosebumps form a niche to regulate hair follicle stem cells

This article is for curiosity and learning only and is not medical advice.