If you are washing grease off your hands then you actually do want to apply the soap/washing up liquid first.
In this way the grease-loving end of the whatever-it-is molecules stick to the grease before the water-loving end gets to adhere to water. You can then remove the grease from your hands using less soap and with less water.
Also you should always silently sing the happy birthday song to yourself whilst washing your hands to make sure enough friction goes on for long enough to get the job done...
Some people are expected to wash their hands a lot, many times a day. These people need to a oid irritation because that defeats hand washing.
"When is clean too clean" (or something like that) is the CDC document.
I've also heard that wet hands then soap makes for better coverage. I'd think that either way would work the same if peoe took enough time and effort with washing.
I would really like to know - with science - what the best method is. I suspect that at one point someone had to write a set of instructions and so that's what we've been doing ever since.
I'm no biology or chemistry expert so I might not have this completely right, but here's how I understand it.
Soaps are a surfactant, when you add water (dilute? You aren't pouring water on it, come on!) you "activate" the soap and that forms micelles. This is the "lather" reaction. This is good, we want this for cleaning.
>. So when you put soap in water, the ends of the soap molecules that are attracted to it latch on right away and the other ends stick straight up in the air. Any soap molecules trapped underneath will fight their way to the surface and eventually you end up with three layers: a layer of soap molecules, a layer of water and another layer of soap molecules pushing themselves away from the main body of water underneath. These three layers form the wall of a bubble .... The different ends of soap molecules are also what make soap so good at cleaning. As you learned earlier, when you mix soap with water, it lowers the surface tension of the water by separating the water molecules, as the soap molecules push up between them. Meanwhile, the other ends of the soap molecules that are attracted to dirt grab on to it. As multiple soap molecules attach themselves to the same piece of dirt, they eventually break it down into tiny particles, which then can easily be washed away
This is most noticed with bar soap, but I still say you can't form a proper lather with liquid soap without wetting your hands first, and it doesn't cover the entirety of your hands (backs, between the fingers) unless you use a TON and I mean a TON of soap.
As an aside, if you have grease on you, either from cooking or mechanical work, apply vegetable oil first and rub it in to cut or thin the grease, then wash with strong detergent and very hot water.
Wearing nitrile gloves where possible might help since it's hard to be sure the grease, solvent and/or detergents you're using aren't toxic or carcinogenic. Both my grandfather and father had the same benign bladder cancer by being exposed to the same compound. It's also a whole lot faster to clean up, because some substances stain the skin for days and cleaning them requires vigorous dermabrasion. That irritation alone is bound to cause other issues.
If you are washing grease off your hands then you actually do want to apply the soap/washing up liquid first.
In this way the grease-loving end of the whatever-it-is molecules stick to the grease before the water-loving end gets to adhere to water. You can then remove the grease from your hands using less soap and with less water.
Also you should always silently sing the happy birthday song to yourself whilst washing your hands to make sure enough friction goes on for long enough to get the job done...