Does soap need bubbles to clean?

This question came from a reader submission (thanks Steve!). Has a curious question stumped you lately? Feel free to submit your own question here:

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📓 The short answer

No. Soap bubbles are merely a byproduct of the cleaning process. You don't need bubbles to know that the soap is cleaning effectively.

📚 The long answer

Scrub-a-dub-bub?

It's a pertinent question for those on dish duty: Do bubbles indicate that soap is cleaning effectively?

Let's begin with a quick lesson on how soap works:

How does soap clean?

We all know that oil and water don't mix, which is why it's nearly impossible to clean greasy dishes with just water. That's where soap comes in.

Soap is a substance that attaches to oils and fats, allowing them to be washed away with water. At a molecular level, soap has a hydrophilic head (bonds with water) and a hydrophobic tail (repels water and bonds with oils and fats).

Diagram of a soap molecule with a hydrophobic head and hydrophilic tail — An overly simplistic diagram of a soap molecule.

When soap mixes with water and grease, soap molecules form structures called micelles (not to be confused with yourcelles 🥁).

Micelles surround particles of oil and fat, with hydrophobic tails bonding to grease and hydrophilic heads attaching to water.

Diagram of a soap micelle forming around grease, while being suspended in water. — A diagram of a soap micelle picking up a particle of grease.

Soap essentially suspends grease, allowing it to be washed away with water. Without soap, water alone wouldn't be able to remove the grease so easily.

Does soap need bubbles to clean?

Nope. Soap suds are just a byproduct of the cleaning process. Bubbles form when air gets stuck between soap and water layers.

Diagram of a layer of soap, water, soap, and air. This forms a bubble. — Designers, please avert your eyes. I didn't know how to make a perfect soap circle in Figma. 😳

Bubbles form easily with soap because it is a natural surfactant, short for "surface active agent". A surfactant reduces the surface tension of water, allowing soap to mix with water and wash away dirt.

With soap's surfactant powers, water becomes more spreadable and prone to forming bubbles. However since soap doesn't need air to attach and lift away grease, bubbles aren't necessary for cleaning.

Interestingly though, many soap and detergent manufacturers add extra surfactants, called sudsing agents, to intentionally create bubbles. This is because consumers associate bubbles with cleaning, so more bubbles make the product seem more effective.

Natural sudsing agents include cocamidopropyl betaine (from coconuts) and octyl glucoside (from the foxglove plant). Common chemically-produced sudsing agents include sodium laureth sulfate and ammonium lauryl sulfate.

🧠 Bonus brain points

What is the difference between soap and detergent?

Soap is made from natural ingredients like plant and animal fats, whereas detergent is synthetic product designed for specific cleaning tasks.

While soap has been around for thousands of years, detergents entered the picture when World War I caused a shortage of soap ingredients. Manufacturers used chemical innovations to meet the demand of soap without requiring highly-sought-after natural ingredients.

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All my best,

Caitlin

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📖 Book of the week

Altered Traits: Science Reveals How Meditation Changes Your Mind, Brain, and Body by Daniel Goleman and Richard J. Davidson

Humans have been practicing meditation for thousands of years. So how much do we know about its impact from a scientific perspective? That's the question this book sets out to answer.

Altered Traits is as much of a book about meditation as it is about conducting research studies. It goes deep into different areas of research that have been explored with meditation, including attention, acts of kindness, physical health, and more, and summarizes what we know (and don't know).

It was interesting to read about all the complexities in this area of research (e.g. which types of meditation were followed?, how long do you have to meditate to be considered a longterm meditator?, etc.), but I did end up skimming it after a while. But if you're a nerd for meta-analysis and meditation, this is the book for you!

Check out the full list of books I've recommended here.