What actually happens when you wash your hands?

How soap works to keep you clean and healthy

Klara Zietlow
5 min readOct 5, 2020
Four brown bars of soap with lavendar in the background
Photo by Aurélia Dubois on Unsplash

In an age of gene therapy and self-driving cars, it is remarkable that an unsoaphisticated thing such as soap and water, an ancient and fundamentally unchanged recipe, remains one of our most powerful weapons against sickness and disease.

Throughout the day we pick up all sorts of dirt, viruses, and microbes which can lead to sicknesses and poor hygiene. But although we use soap everyday, many of us don’t know why it works. Don’t worry, I’ve been there too. So, water you waiting for? Let me explain…

p.s. Sorry for the puns, but I promise that they’re all clean ;)

What is soap?

Our farthest records of soap trace back almost 5,000 years to the ancient Babylonians who made it by boiling together animal fat and ash or lye. Over time, it spread around the world inheriting local twists such as the type of fat and essential oils used.

What might be soaprising though, is that our modern methods of making soap follow the same ancient principles. Although synthetic chemicals are now more common than whale blubber and beef tallow 😉

But the secret to what makes it soapowerful against grime is in its hybrid structure. Soap is made up of lollipop-shaped molecules 🍭, each containing a candy head attracted to water and a stick tail that prefers fatty, greasy substances. We call these two components hydrophilic meaning “water-loving” and hydrophobic, “water-fearing.”

But like, how does it clean?

By themselves, water and oil don’t mix — imagine an oil spill on top of a lake — which is why washing your hands with only water isn’t very effective. In order for oil (which attracts dirt) to mix with water, it needs an emulsifier to help it. (Think of egg yolks in mayonnaise to keep the oil blended with the water.)

Luckily, soaps hybrid structure is just that.

A diagram showing a micelle
Micelle made of soap molecules surrounding dirt | SuperManu on Wikimedia Commons [CC BY-SA]

When soap, water, and dirt are all lathered up together on your hands, the molecules get to work. At first, the little lollipops float around by themselves. But once they locate a piece of fat, they congregate around it in little bubbles called micelles.

Then they jab their fat-loving tails into the dirt and stick their heads out towards the water. When the faucet rushes over them, the candy heads attach to the water and the entire micelle washes away down the drain. Yay! 🚿

Soap vs. Virus

Many bacteria and viruses, including coronavirus, are encased in a lipid (fat) membrane. This protein embedded casing (labeled Envelope in the diagram below) helps the virus to infect host cells and protects the fragile genetic information that allows them to reproduce.

A diagram showing features of the coronavirus
Coronavirus structure by scientificanimations/wiki-images | Creative Commons BY-SA (Attribution-ShareAlike 4.0 International)

Soap far so good? When soap comes in contact with a virus on your skin, the hydrophobic tails of the soap molecules attempt to escape water by wedging themselves into the outer membrane of the virus, prying it apart.

“They act like crowbars and destabilize the whole system,” said Prof. Pall Thordarson, acting head of chemistry at the University of New South Wales. The delicate genetic information spills from the shattered membrane where it washes away with the help of other micelles. 🧹

Can I use hand sanitizer or antibacterial soap?

Hand sanitizer with at least 60% alcohol works similarly to soap in that it also deactivates viruses. But instead of breaking apart their fatty casing, it dissolves it. It doesn’t work quite as well as hand washing though because although it can destabilize the viruses, it can’t remove them from your skin.

In addition, not all viruses have lipid membranes and certain bacteria protect themselves with a sturdy armor 🛡️⚔️ of protein and sugar. Some examples include: norovirus, poliovirus, as well as the bacteria that cause meningitis and pneumonia.

In general, these microbes are usually lather indifferent to ethanol and soap, yet vigorous scrubbing with soap and water can still dislodge them from your skin. Because of this, the CDC recommends hand-washing over using sanitizer. Hand sanitizer is still a good choice for when you’re out and about though.

You’d think that with such a fancy name, antibacterial soap would keep you cleaner than regular soap. That’s a lye! There isn’t enough science to prove it works any better than normal soap, so you can skip it. ❌

A man in a white shirt washing his hands

A wonderful thing

Although soap is many things, it’s important to understand that it’s not instant. It takes time for soap molecules to form micelles and break apart viruses. To wash your hands work up a nice lather, scrub your palms, the back of your hands, between your fingers, around your thumbs, and twist a sudsy hand around your wrists.

Or do as the Round Rock city council advises, “Wash your hands like you just got done slicing jalapeños for a batch of nachos and you need to take your contacts out.” 🌮👀

That’s at least 20 seconds of scrubbing or the chorus of Lizzo’s “Truth Hurts.”

Next time you have the urge to walk past the sink, remember: Other people’s lives are in your hands.

Key Takeaways:

  • Soap molecules have two different sides, one attracted to water and the other to fat which act as an emulsifier to connect fat on your skin with water from the faucet
  • Hand sanitizer is a good option for when you’re on the go, but it shouldn’t replace actual hand washing
  • Soap needs time in order to work so make sure to scrub intensely for at least 20 seconds

🛑 Before you go, I’m a 13-year-old passionate about a more sustainable future and I’d love to connect on LinkedIn or by email (klaradzietlow@gmail.com). If you found value in this article👏 it and post your takeaways in the comments!

Stay safe everyone! ❤



Klara Zietlow

Passionate about the future of food and the environment. Likes animals too :)