When I’m in the shower, sometimes I’ll notice my hair is particularly greasy and once I’ve rinsed off the first round of shampoo, I’ll apply a second round. And no matter how small of an amount I apply the second time around, it turns into a baby bubble bath commercial with oodles of suds and bubbles and foam all over the place?
Is it because the first lot got used up on a larger bulk of grease and the second amount doesn’t and so it can bubble up more?
In: Chemistry
LabMuffin on YouTube just answered this in a recent video! I can’t remember the exact reason unfortunately lol but go check her out
Shampoo molecules have one end that binds to water (hydrophilic head) and another one that binds to sebum/grease (hydrophobic tail).
Bubbles form because the shampoo molecule reduces the surface tension of the water when it binds to it. But when it also binds to something else on the other end it cancels out that effect.
During the second round most tails have nothing to bind with, so a lot of bubbles can freely form.
Basically the first time most of it is stuck to dirt and oil, so it’s not available to make bubbles. The second time it’s a lot less, so more bubbles!
Yes it’s what you said. Soap binds to dirt and grease. Free unused soap makes bubbles. Soap particles that have grabbed a piece of dirt or grease can’t participate in bubble making.
On the first wash most of the soap gets used up removing the grease, so it’s bound up and can’t foam. If you shampoo again there’s less grease to bind up the soap, so it can foam more.
I never bothered looking into the exact science, but I had the same observations and came to the same conclusion. It’s why I always shampoo twice! That bubbly foamy feeling reassures me my hair is clean.
I’m reusing one of my comments from a similar post a while back cause I’m lazy
Shampoo lathers less when your hair is dirty because the surfactant that causes lather is grabbing all the dirty stuff and holding it. The second wash your hair is cleaner so it lathers more. It doesn’t improve cleaning ability, but a second wash might get out stuff the first wash didn’t. It’s just not cleaning “harder”
First shampoo is basically just loosening the grease and dirt and the second is the one that actually removes dirt. So even when the first one isn’t lathering you should still continue to scrub/massage as normal.
I’ve never heard of applying a shampoo twice, is this a normal thing?
Part of it is marketing genius.
WSJ article from 1979
[https://www.washingtonpost.com/archive/lifestyle/magazine/1979/12/30/double-bubble/5708142c-d880-48fa-b4d5-bcc88125ab2f/](https://www.washingtonpost.com/archive/lifestyle/magazine/1979/12/30/double-bubble/5708142c-d880-48fa-b4d5-bcc88125ab2f/)
Thanks for asking the question. It’s strange because I was wondering the same thing myself just yesterday, and wondered if Reddit would answer the question.
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