[JDavidJ (OP)]

Perhaps topical at the moment, a hand-washing question:

When washing my hands with liquid soap, I always smear it on before adding a bit of water, as it sticks better that way. If it's water first, the soap often just slides off. Yet the official guidelines, widely published, always state to wet hands first. Is there a scientific reason for this, or is it just a meme with no foundation?

(By the way when hand-washing in public lavatories I always check that the water is working before I soap-up, having been caught out on odd occasions.)

[alancalverd]

I always start with liquid soap or gel, but water first if using bar soap, which doesn't rub off easily onto dry skin.

[vhfpmr]

I always start with liquid soap or gel, but water first if using bar soap, which doesn't rub off easily onto dry skin.

Ditto

The instructions on Swarfega explicitly say apply to dry hands, and with good reason, it doesn't work at all well if you wet them first. It seems to me that a film of water will create a barrier between the soap and the dirt, when my understanding is that soaps are molecules that bind to dirt on one side and water on the other.

[alancalverd]

Correct.

[Janus]

I always start with liquid soap or gel, but water first if using bar soap, which doesn't rub off easily onto dry skin.

Ditto

The instructions on Swarfega explicitly say apply to dry hands, and with good reason, it doesn't work at all well if you wet them first. It seems to me that a film of water will create a barrier between the soap and the dirt, when my understanding is that soaps are molecules that bind to dirt on one side and water on the other.

If you are not rubbing your hands together vigorously enough or long enough for that to make a difference, you aren't doing a proper job in washing your hands.
It is the physical rubbing of your hands together that does the most good in removing dirt, grime, and associated germs from your hands.

[alancalverd]

Simply rubbing greasy hands together just redistributes the grease. You need a surfactant to form hydrophilic micelles that actually take it into aqueous suspension, along with the bugs therein. Rubbing improves the contact between surfactant and grease, and also ensures that the surfactant penetrates the cracks and creases, though scrubbing is even more effective, particularly for knuckles and under fingernails.

Nevertheless in the case of snot-borne infections, warm water alone is better than nothing if the droplets are still fresh, as sputum and phlegm are miscible with water.

[JDavidJ (OP)]

While all the replies are true, none of them address my question of the basis of the instruction in public washing places, to wet hands first.  I'm afraid this thread feels very like the way Microsoft support (or politicians) respond to questions - they answer something of their own choice rather than what was asked.

[Colin2B]

The problem with instructions is they have to be simple and cover all circumstances, so wetting hands first covers both bar and liquid soaps. Also, even if liquid soap is applied first it doesn't spread so easily on dry skin as on wet and the idea is to get an even and thorough coverage.

[alancalverd]

Politicians and civil servants live in a past century, before liquid soap.

[Colin2B]

Politicians and civil servants live in a past century, before liquid soap.

You missed out HSE executives, are you slipping or just trying to wash your hands of them?

[vhfpmr]

I always start with liquid soap or gel, but water first if using bar soap, which doesn't rub off easily onto dry skin.

Ditto

The instructions on Swarfega explicitly say apply to dry hands, and with good reason, it doesn't work at all well if you wet them first. It seems to me that a film of water will create a barrier between the soap and the dirt, when my understanding is that soaps are molecules that bind to dirt on one side and water on the other.

If you are not rubbing your hands together vigorously enough or long enough for that to make a difference, you aren't doing a proper job in washing your hands.
It is the physical rubbing of your hands together that does the most good in removing dirt, grime, and associated germs from your hands.

When I get my fingers greasy off the bike at the side of the road I use the nearest paving or brick wall as a pumice. It's very effective at getting enough grease off to keep handlebars and gloves clean, but you can still see black lines in the grooves of your fingerprint. It takes something to act as a solvent to get that out.

At home I put Rozalex on before I start work, that seems to work even though the white spirit I use to clean the bike appears to wash it all off my hands.

[Bored chemist]

. It seems to me that a film of water will create a barrier between the soap and the dirt, when my understanding is that soaps are molecules that bind to dirt on one side and water on the other.

If 20 seconds of rubbing your hands together doesn't break down any such barrier, you are doing it badly wrong.

Politicians and civil servants live in a past century, before liquid soap.

LOL
Who do you think  actually did the work on which  all the advice is based?

(BTW, just a quick hint; Were they paid by the government (i.e. are they government servants) and are they military (i.e. not civilian servants)?

[alancalverd]

LOLWho do you think  actually did the work on which  all the advice is based?

"All the advice" seems to be not to sneeze over others, clean all surfaces (Nightingale, 1854) and wash your hands often (Semmelweiss, 1840) just as your mum told you.

We note that the advice of successive politicians and civil servants to outsource hospital cleaning has now led to the cleaners at Lewisham Hospital walking out as they haven't been paid for 2 months. I don't recall any clinical scientist, doctor or nurse making such an absurd recommendation.     

[alancalverd]

You missed out HSE executives,

Along with  CQC inspectors, they live on a different planet, where the laws of physics are something you make up as you go along, regardless of the facts. The folk who really understand infection control seem to be local authority food safety inspectors, but HM Government  regards local authorities as a waste of money.

[Bored chemist]

We note that the advice of successive politicians and civil servants to outsource hospital cleaning

How did you come to the conclusion that the civil service gave that advice?

"All the advice" seems to be

You plainly need to read the rest of it  if that's how it seems to you.

[alancalverd]

The advice to outsource hospital cleaning came in directives from the Thatcher government via the Treasury, which as I recall is staffed by civil servants. Not that they are all incompetent: my colleagues in the Department of Health recognised the stupidity of the order. If you outsource  a critical element of your quality system, you lose control of cost or quality - or both, in the case of PFI buildings. And as Florence herself explained, cleaning is critical to recovery.

"Isolation" has its origins in Leviticus, along with food hygeine. Come to think of it, so does travel restriction!

[strongernow]

Simply rubbing greasy hands together just redistributes the grease. You need a surfactant to form hydrophilic micelles that actually take it into aqueous suspension, along with the bugs therein. Rubbing improves the contact between surfactant and grease, and also ensures that the surfactant penetrates the cracks and creases, though scrubbing is even more effective, particularly for knuckles and under fingernails.

Nevertheless in the case of snot-borne infections, warm water alone is better than nothing if the droplets are still fresh, as sputum and phlegm are miscible with water.

Really interesting and important topic nowadays! Hand hygiene should be discussed more in public places like school and work places.

[Natalie Roberts]

I use foaming hand soap. Do you just pump this in your hand than start washing them with no water? just start rubbing as usual then use water to rinse?? Is that right?