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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Soap isn’t really meant to kill germs, it’s meant to make things slippery so that the germs slide off your hands into the sink when you rinse it off.
Neither actually soaks in. Hand sanitizer just leaves your hands as it evaporates.
The soap grabs onto oils as it passes and drags them along with it. A good scrubbing helps to get the soap into cracks and break the particles free.
Soap is a special compound.
Oil and Water normally cannot mix. Oil is a non-polar molecule. Water is a polar molecule. Polar and non-polar cannot mix. Enter Soap.
Through a chemical process, soap is a molecule that has a polar component to it as well as a non-polar component of it. So you rub on the soap and the non-polar portion of the soap binds with the oils on your skin and then when you rinse with water, the polar portion of soap is caught up by the water and washed away, taking the oils with it. This is how soap works.
Hand sanitizer evaporates, or at least the alcohol component that does the bulk of the sanitizing does.
Soap and the physical abrasion of scrubbing your hands damages cell walls, killing the microbes. The assorted gunk of those destroyed microbes, dirt, oils, etc… Is also loosened and suspended in the suds so it can be washed away readily with water.
There’s only so much the soap can do, leaving it longer doesn’t help much, but if you fail to wash it away most of that crud and any surviving microbes are left on your hands as food for the next batch of germs.
This is actually one of the big problems with sanitizer, it doesn’t take things away like properly washing and rinsing does and many of them leave residual oils or other substances added for scent or whatever. That’s fine for a quick touch up now and then but does not at all replace regular hand washing to get rid of all that.
I’m not an expert in this field by any means but this is my rough understanding of what happens
First of all, hand sanitizer does not soak in either, rather it evaporates due to the high percentage of alcohol, which also kills bacteria (and not viruses AFAIK).
Bar soap contains molecules that has one end that is attracted to water and the other that is attracted to lipids (fats). The lipid side will attach itself to the lipid surface of the germ and when you go to rinse with water, the side that is attracted to water will basically cause these molecules to rip out of the germ, destroying it in the process.
Liquid soap does not contain those molecules so, unless oral anti-bacterial, it’s really more to wash the dirt off your hands than anything else. Furthermore, antibacterial soap only kills bacteria and not viruses. I’ve seen studies where it was proposed that you do not use antibacterial soap because it could help increase the chances of antibiotic resistant bacteria developing.
Oh I love this one.
So, soap molecules are pretty cool. One side of the molecule is afraid of water, and sticks to fats/oils/lipids/dirt. The other side is afraid of fats/oils/lipids/dirt, and sticks to water.
So, you lather up some soap, and what’s happening is you’re dispersing a ton of these molecules.
Say you’ve got some cooking oil on your hands. You lather up some soap on your hands, and the soap molecules will completely surround the oil molecule, covering it entirely.
Now, the oil is trapped by the soap molecules, and the side that sticks to fat is all pointed at the oil molecule. So, the side that sticks to water, is sticking out in all directions from that oil molecule.
This makes it easy to wash away off of you and down the drain.
Bonus: Virus have outer coatings of fat. Washing your hands with basic soap clears you skin of viruses because they get treated exactly like the oil molecule.
I remember figuring this out my messing around in the kitchen. When I was a kid
Grab a bottle, add oil and water. Weird how they don’t mix at all no matter how hard you shake them.
Add soap. Then they are able to combine.
That’s soaps job. It takes oils and dirt that isn’t normally soluble in water and allows for it to be easily mixed with water, which you can then rinse off your hands.
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.
One (quite gross) metaphor that stuck with me when we all learned a LOT about handwashing in 2020 was: say you have rats (bacteria) in your cellar. Hand sanitizer is like putting poison down: it kills them all but you still have a cellar full of dead rats. Soap is like opening up the drain and using a firehose: it doesn’t matter if they’re not all dead, they’re simply not in your cellar any more.
The germs stick to the soap. Then you rinse the soap and the germs down the sink with water.
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