how does soap work if we put it on our hands and then take it off immediately? It doesn’t soak in like hand sanitizer
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You know how water and oil don’t mix? If you don’t, you can take a glass of water, and pour a bit of cooking oil in. The oil won’t mix in with the water, it will sort of sit on top (which is also how we get oil slicks when there are massive oil spills).
Well it turns out a lot of the smelly icky stuff on your skin is oily! But oh no! Since we as humans need to drink (clean) water to survive we have put running taps with water in our homes, but when we use those to rinse off, the oily stuff won’t mix in with the water, and the water will just slide over it, leaving it behind. What a bother!
Fortunately we have the wonder of soap: soap molecules are special because they have both an oily end *and* a watery end.
So if you moisten your hands first, and also rinse off the icky bits that do mix wityh water, then apply soap so it can dissolve in the little amount of water that is on your hands still, really rub it in, so you mix it with the icky oily bits.
Now, when you wash your hands with water, the oil won’t mix with it, but it has mixed with the soap, and the soap will mix with the water, so the oily stuff will rush along with the water! Excellent, your skin is all clean now!
If you are interested in the technical terms the “watery” stuff is called polar (or hydrophilic, from greek: hydro- means water, and -phile means lover), and the “oily” stuff is called apolar (or hydrophobic, -phobia means fear).
u/d4m1ty has the same explanation [here.](https://old.reddit.com/r/explainlikeimfive/comments/107rlxm/eli5_how_does_soap_work_if_we_put_it_on_our_hands/j3o2a6l/)
If you are wondering why there are only two groups of stuff in this context, polar stuff has a polarity, where one end is more elctrically charged than the other (in H2O, the O is slightly negative, and the Hs slightly positive), where as apolar stuff has no polarity, the charges (electrons) are distributed equally in the molecule.
A molecule can be strongly polar or have a weak polarity, but in both cases, it has a polarity, and won’t mix with stuff that has no polartiy.
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