Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to CuriousKidsUS@theconversation.com.

How does soap clean our bodies? – Charlie H., age 8, Stamford, Connecticut

Thousands of years ago, our ancestors discovered something that would clean their bodies and clothes. As the story goes, fat from someone’s meal fell into the leftover ashes of a fire. They were astonished to discover that the blending of fat and ashes formed a material that cleaned things. At the time, it must have seemed like magic.

That’s the legend, anyway. However it happened, the discovery of soap dates back approximately 5,000 years, to the ancient city of Babylon in what was southern Mesopotamia – today, the country of Iraq.

As the centuries passed, people around the world began to use soap to clean the things that got dirty. During the 1600s, soap was a common item in the American colonies, often made at home. In 1791, Nicholas Leblanc, a French chemist, patented the first soapmaking process. Today, the world spends about US$50 billion every year on bath, kitchen and laundry soap.

But although billions of people use soap every day, most of us don’t know how it works. As a professor of chemistry, I can explain the science of soap – and why you should listen to your mom when she tells you to wash up.

The chemistry of clean

Water – scientific name: dihydrogen monoxide – is composed of two hydrogen atoms and one oxygen atom. That molecule is required for all life on our planet.

Chemists categorize other molecules that are attracted to water as hydrophilic, which means water-loving. Hydrophilic molecules can dissolve in water.

So if you were to wash your hands under a running faucet without using soap, you’d probably get rid of lots of whatever hydrophilic bits are stuck to your skin.

But there is another category of molecules that chemists call hydrophobic, which means water-fearing. Hydrophobic molecules do not dissolve in water.

Oil is an example of something that’s hydrophobic. You probably know from experience that oil and water just don’t mix. Picture shaking up a jar of vinaigrette salad dressing – the oil and the other watery ingredients never stay mixed.

So just swishing your hands through water isn’t going to get rid of water-fearing molecules such as oil or grease.

Here’s where soap comes in to save the day.

Soap, a complex molecule, is both water-loving and water-fearing. Shaped like a tadpole, the soap molecule has a round head and long tail; the head is hydrophilic, and the tail is hydrophobic. This quality is one of the reasons soap is slippery.

It’s also what gives soap its cleaning superpower.

A microscopic view

To see what happens when you wash your hands with soap and water, let’s zoom in.

Picture all the gunk that you touch during the day and that builds up on your skin to make your hands dirty. Maybe there are smears of food, mud from outside, or even sweat and oils from your own skin.

All of that material is either water-loving or water-fearing on the molecular level. Dirt is a jumbled mess of both. Dust and dead skin cells are hydrophilic; naturally occurring oils are hydrophobic; and environmental debris can be either.

If you use only water to clean your hands, plenty will be left behind because you’d only remove the water-loving bits that dissolve in water.

But when you add a bit of soap, it’s a different story, thanks to its simultaneously water-loving and water-fearing properties.

Soap molecules come together and surround the grime on your hands, forming what’s known as a micelle structure. On a molecular level, it looks almost like a bubble encasing the hydrophobic bit of debris. The water-loving heads of the soap molecules are on the surface, with the water-fearing tails inside the micelle. This structure traps the dirt, and running water washes it all away.

To get the full effect, wash your hands at the sink for at least 20 seconds. Rubbing your hands together helps force the soap molecules into whatever dirt is there to break it up and envelope it.

It’s not just dirt

Along with dirt, your body is covered by microorganisms – bacteria, viruses and fungi. Most are harmless and some even protect you from getting sick. But some microorganisms, known as pathogens, can cause illness and disease.

They can also cause you to smell if you haven’t taken a bath in a while. These bacteria break down organic molecules and release stinky fumes.

Although microorganisms are protected by a barrier – it’s called a membrane – soap and water can disrupt the membrane, causing the microorganism to burst open. The water then washes the remains of the microorganism away, along with the stink.

To say that soap changed the course of civilization is an understatement. For thousands of years, it’s helped keep billions of people healthy. Think of that the next time Mom or Dad asks you to wash up – which will likely be sometime soon.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

Paul E. Richardson, Professor of Biochemistry, Coastal Carolina University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to CuriousKidsUS@theconversation.com.

Why don’t humans have hair all over their bodies like other animals? – Murilo, age 5, Brazil

Have you ever wondered why you don’t have thick hair covering your whole body like a dog, cat or gorilla does?

Humans aren’t the only mammals with sparse hair. Elephants, rhinos and naked mole rats also have very little hair. It’s true for some marine mammals, such as whales and dolphins, too.

Scientists think the earliest mammals, which lived at the time of the dinosaurs, were quite hairy. But over hundreds of millions of years, a small handful of mammals, including humans, evolved to have less hair. What’s the advantage of not growing your own fur coat?

I’m a biologist who studies the genes that control hairiness in mammals. Why humans and a small number of other mammals are relatively hairless is an interesting question. It all comes down to whether certain genes are turned on or off.

Hair benefits

Hair and fur have many important jobs. They keep animals warm, protect their skin from the sun and injuries and help them blend into their surroundings.

They even assist animals in sensing their environment. Ever felt a tickle when something almost touches you? That’s your hair helping you detect things nearby.

Humans do have hair all over their bodies, but it is generally sparser and finer than that of our hairier relatives. A notable exception is the hair on our heads, which likely serves to protect the scalp from the sun. In human adults, the thicker hair that develops under the arms and between the legs likely reduces skin friction and aids in cooling by dispersing sweat.

So hair can be pretty beneficial. There must have been a strong evolutionary reason for people to lose so much of it.

Why humans lost their hair

The story begins about 7 million years ago, when humans and chimpanzees took different evolutionary paths. Although scientists can’t be sure why humans became less hairy, we have some strong theories that involve sweat.

Humans have far more sweat glands than chimps and other mammals do. Sweating keeps you cool. As sweat evaporates from your skin, heat energy is carried away from your body. This cooling system was likely crucial for early human ancestors, who lived in the hot African savanna.

Of course, there are plenty of mammals living in hot climates right now that are covered with fur. Early humans were able to hunt those kinds of animals by tiring them out over long chases in the heat – a strategy known as persistence hunting.

Humans didn’t need to be faster than the animals they hunted. They just needed to keep going until their prey got too hot and tired to flee. Being able to sweat a lot, without a thick coat of hair, made this endurance possible.

Genes that control hairiness

To better understand hairiness in mammals, my research team compared the genetic information of 62 different mammals, from humans to armadillos to dogs and squirrels. By lining up the DNA of all these different species, we were able to zero in on the genes linked to keeping or losing body hair.

Among the many discoveries we made, we learned humans still carry all the genes needed for a full coat of hair – they are just muted or switched off.

In the story of “Beauty and the Beast,” the Beast is covered in thick fur, which might seem like pure fantasy. But in real life some rare conditions can cause people to grow a lot of hair all over their bodies. This condition, called hypertrichosis, is very unusual and has been called “werewolf syndrome” because of how people who have it look.

In the 1500s, a Spanish man named Petrus Gonsalvus was born with hypertrichosis. As a child he was sent in an iron cage like an animal to Henry II of France as a gift. It wasn’t long before the king realized Petrus was like any other person and could be educated. In time, he married a lady, forming the inspiration for the “Beauty and the Beast” story.

While you will probably never meet someone with this rare trait, it shows how genes can lead to unique and surprising changes in hair growth.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

Maria Chikina, Assistant Professor of Computational and Systems Biology, University of Pittsburgh

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.

Are twins allergic to the same things? – Ella, age 7, Philadelphia

Allergies, whether spring sneezes due to pollen or trouble breathing triggered by a certain food, are caused by a combination of someone’s genes and the environment they live in.

The more things two people share, the higher their chances of being allergic to the same things. Twins are more likely to share allergies because of everything they have in common, but the story doesn’t end there.

I’m an allergist and immunologist, and part of my job is treating patients who have environmental, food or drug allergies. Allergies are really complex, and a lot of factors play a role in who gets them and who doesn’t.

What is an allergy?

Your immune system makes defense proteins called antibodies. Their job is to keep watch and attack any invading germs or other dangerous substances that get inside your body before they can make you sick.

An allergy happens when your body mistakes some usually harmless substance for a harmful intruder. These trigger molecules are called allergens.

The antibodies stick like suction cups to the allergens, setting off an immune system reaction. That process leads to common allergy symptoms: sneezing, a runny or stuffy nose, itchy, watery eyes, a cough. These symptoms can be annoying but minor.

Allergies can also cause a life-threatening reaction called anaphylaxis that requires immediate medical attention. For example, if someone ate a food they were allergic to, and then had throat swelling and a rash, that would be considered anaphylaxis.

The traditional treatment for anaphylaxis is a shot of the hormone epinephrine into the leg muscle. Allergy sufferers can also carry an auto-injector to give themselves an emergency shot in case of a life-threatening case of anaphylaxis. An epinephrine nasal spray is now available, too, which also works very quickly.

A person can be allergic to things outdoors, like grass or tree pollen and bee stings, or indoors, like pets and tiny bugs called dust mites that hang out in carpets and mattresses.

A person can also be allergic to foods. Food allergies affect 4% to 5% of the population. The most common are to cow’s milk, eggs, wheat, soy, peanuts, tree nuts, fish, shellfish and sesame. Sometimes people grow out of allergies, and sometimes they are lifelong.

Who gets allergies?

Each antibody has a specific target, which is why some people may only be allergic to one thing.

The antibodies responsible for allergies also take care of cleaning up any parasites that your body encounters. Thanks to modern medicine, people in the United States rarely deal with parasites. Those antibodies are still ready to fight, though, and sometimes they misfire at silly things, like pollen or food.

Hygiene and the environment around you can also play a role in how likely it is you’ll develop allergies. Basically, the more different kinds of bacteria that you’re exposed to earlier in life, the less likely you are to develop allergies. Studies have even shown that kids who grow up on farms, kids who have pets before the age of 5, and kids who have a lot of siblings are less likely to develop allergies. Being breastfed as a baby can also protect against having allergies.

Children who grow up in cities are more likely to develop allergies, probably due to air pollution, as are children who are around people who smoke.

Kids are less likely to develop food allergies if they try foods early in life rather than waiting until they are older. Sometimes a certain job can contribute to an adult developing environmental allergies. For example, hairdressers, bakers and car mechanics can develop allergies due to chemicals they work with.

Genetics can also play a huge role in why some people develop allergies. If a mom or dad has environmental or food allergies, their child is more likely to have allergies. Specifically for peanut allergies, if your parent or sibling is allergic to peanuts, you are seven times more likely to be allergic to peanuts!

Identical in allergies?

Back to the idea of twins: Yes, they can be allergic to the same things, but not always.

Researchers in Australia found that 60% to 70% of twins in one study both had environmental allergies, and identical twins were more likely to share allergies than fraternal (nonidentical) twins. Identical twins share 100% of their genes, while fraternal twins only share about 50% of their genes, the same as any pair of siblings.

A lot more research has been done on the genetics of food allergies. One peanut allergy study found that identical twins were more likely to both be allergic to peanuts than fraternal twins were.

So, twins can be allergic to the same things, and it’s more likely that they will be, based on their shared genetics and growing up together. But twins aren’t automatically allergic to the exact same things.

Imagine if two twins are separated at birth and raised in different homes: one on a farm with pets and one in the inner city. What if one’s parents smoke, and the others don’t? What if one lives with a lot of siblings and the other is an only child? They certainly could develop different allergies, or maybe not develop allergies at all.

Scientists like me are continuing to research allergies, and we hope to have more answers in the future.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

Breanne Hayes Haney, Allergy and Immunology Fellow-in-Training, School of Medicine, West Virginia University

This article is republished from The Conversation under a Creative Commons license. Read the original article.