Cold water vs. hot

[Bushranger]

I frequently see the signs in restrooms, "Employees must wash their hands with hot water and soap before returning to work.", which for me begs the question: Given that germs are not likely to be killed by the relatively tepid temperature that a human's hands can withstand, why use hot water versus cold water?  Is there any scientific reason the hot water and soap will be more effective in removing germs than cold water and soap?

[DrP]

Maybe the surfactants work better and quicker in hot water vs cold water?.... They act physically on the molecular level forming micelles around the dirt, which I can see forming faster and easier in warm water over cold, but Really, I am not sure if it would make much of a difference.  They will still work in cold water and washing in cold water will be better than not washing your hands at all.

 

 

[studiot]

Grease and oils form a barrier that is more easily removed by hot (soapy) water.

[Strange]

I'm fairly sure I read an article recently about research showing that hot water was no more effective than cold at removing germs. I will see if I can find it again...

Here http://www.bbc.co.uk/news/health-40118539

As they say, it is more important how you wash them. 

[Bushranger]

29 minutes ago, Strange said:

I'm fairly sure I read an article recently about research showing that hot water was no more effective than cold at removing germs. I will see if I can find it again...

Here http://www.bbc.co.uk/news/health-40118539

As they say, it is more important how you wash them. 

As I suspected..."...Use hot water..." is a platitude passed along as fact when it is not... like so many other things in our, average I.Q =100 society.

Edited December 1, 2017 by Bushranger

[DrP]

37 minutes ago, studiot said:

Grease and oils form a barrier that is more easily removed by hot (soapy) water.

Yes - but why? Reduced viscosity of the oils? Faster acting and reduced viscosity of the surfactants? Both reasons? More?

My guess then is - reduced viscosity of the oils making it easier for the surfactant molecules to move to their positions...  takes less energy for them to physically do so. The action of the surfactant is a physical process, which is sped up or made more efficient due to the thermal energy in the system. Lathers better basically...  but this is speculation....  and I suspect the hot vs cold water only provides a subtle difference - you can easily wash your hands in cool soapy water - it still works.

Edited December 1, 2017 by DrP

[Strange]

Well, it does "feel" like it should be true. But that is why we use science!

And, as studios says, it will probably be true for oil and grease.

[DrP]

1 minute ago, Strange said:

Well, it does "feel" like it should be true. But that is why we use science!

Yea - I think what I said makes sense - but I have done no measured experiments - it is assumption.  I think the reasons I stated feasibly explain why....  but as I said - it is speculation.

And cold water does work - even if not as well, but by what amount the warmth improves the process I am not sure.

[Phi for All]

I've also heard there are proponents of cold water shaving, which seems intuitively wrong, or like something you should only have to do when conditions force it. They say the skin contracts under the cold water, which causes less irritation (less swelling due to heat?) and exposes more of the hair follicle to the razor. 

[Roamer]

Warm water generally does a better job removing filth stuck to your skin,

and, as employees are supposed to look clean/attractive to customers, it makes sense to make them use hot water.

[Strange]

Just now, Roamer said:

Warm water generally does a better job removing filth stuck to your skin,

But does it, that's the question.

[Roamer]

3 minutes ago, Strange said:

But does it, that's the question.

Usually it does, since usually a higher temperature means a higher solubility, though it depends on the type of filth involved.

[CharonY]

The efficiency of removing germs are primarily dependent on the use of soap and the length (and thoroughness) of your wash. Warm water increases the likelihood of compliance (i.e. washing your hands longer) as with cold water it may become uncomfrotable for some folks.

[DrP]

14 minutes ago, CharonY said:

The efficiency of removing germs are primarily dependent on the use of soap and the length (and thoroughness) of your wash. Warm water increases the likelihood of compliance (i.e. washing your hands longer) as with cold water it may become uncomfrotable for some folks.

I agree - but the question is how much more efficient is it? Is it really necessary to demand hot water when washing in cold water WILL work?...  as you suggested it will have more to do with the amount of soap used and the thoroughness/lenth of time scrubbing than the temperature....  probably.

Edited December 1, 2017 by DrP

[Strange]

13 minutes ago, CharonY said:

Warm water increases the likelihood of compliance (i.e. washing your hands longer) as with cold water it may become uncomfrotable for some folks.

Good point!

[CharonY]

2 minutes ago, DrP said:

I agree - but the question is how much more efficient is it? Is it really necessary to demand hot water when washing in cold water WILL work?...  as you suggested it will have more to do with the amount of soap used and the thoroughness/lenth of time scrubbing than the temperature....  probably.

Yes, if you wash the same time with cold water and soap, it is as efficient in reducing bacterial load. The important bit is to work the soap in thoroughly followed by extensive rinsing and scrubbing.  A good antibacterial wash can take 1-5 minutes. 

[DrP]

20 minutes ago, CharonY said:

Yes, if you wash the same time with cold water and soap, it is as efficient in reducing bacterial load. The important bit is to work the soap in thoroughly followed by extensive rinsing and scrubbing.  A good antibacterial wash can take 1-5 minutes. 

Then maybe the demand for the use of hot water is for the employees comfort, ensuring that they spend longer scrubbing in comfort rather than hurrying the process due to the cold.

 

[CharonY]

That is what I said.

[DrP]

3 minutes ago, CharonY said:

That is what I said.

   -  sort off. You said it would be more comfortable...  but not why the employers have insisted their employees use hot water.

OK - reading back you DID imply that, so, sorry.   

 

[CharonY]

No problem, it was what I meant with compliance. Though I see that I could have written it more clearly.

[fiveworlds]

Quote

Grease and oils form a barrier that is more easily removed by hot (soapy) water.

Grease and oils are removed by soap. Warm soap may remove the grease and oils better but the water is only to wash off the soap (and probably isn't the best liquid for doing that alcohols would probably be more hygenic)

 

Edited December 1, 2017 by fiveworlds