Naked Science Forum

General Science => General Science => Topic started by: apratact0 on 21/07/2018 23:45:25

Title: How does soap make us more clean than just water does?
Post by: apratact0 on 21/07/2018 23:45:25

Why exactly do we use soap on our hands when washing instead of just water?   I know soap removes oil and that soap is hydrophobic.   But how does this correlate to removing germs and bacteria from our hands?  Why dont we just use plain water?   Basically.. How does soap work and what is doing to remove germs?  Not antibacterial soap.  Just plain old soap

Same thing with shampoos and body wash, etc.   Why do we wash our hair with shampoo, how does it make us cleaner besides just removing oils? 

We use soap on our bodies as well to make us smell better..  Why?  Does rinsing away these oils on our bodies have something to do with make us cleaner?

Title: Re: How does soap make us more clean than just water does?
Post by: evan_au on 22/07/2018 03:35:54

Quote from: apratact0

I know soap removes oil and that soap is hydrophobic.

The hydrophobic part is only half of the story.

In fact, soap has a hydrophobic (water-avoiding/non-polar) end, and a hydrophilic (water-loving/polar) end.
- Oils tend to be water-avoiding.

This means that the soap grabs the oils (hydrophobic end), and also grabs the water (hydrophilic end), and gets them together, so that water is able to break down oil films and wash away the oils, instead of the oils staying stubbornly in place.

Soap will help water wash away some bacteria too, but the main thing here is to scrub under running water.
See: https://en.wikipedia.org/wiki/Detergent

In reality, natural oils are helpful to our skin and hair, and overuse of soap and detergents can remove these helpful oils.

But in a hospital setting, presence of drug-resistant bacteria (eg Staphylococcus aureus) and fungi (eg Candida auris) around people with weakened immune systems means that you can't have too much hand-washing.

Title: Re: How does soap make us more clean than just water does?
Post by: Bored chemist on 22/07/2018 10:53:13

Many of the bacteria make their homes in the grease/ oil.
Also, the surface of a bacterium is typically "oily"- and the soap sometimes disrupts that.
The so-called "quat" disinfectants are quite similar to soap (though they have the opposite charge) and they do an even better job of killing bacteria.

https://en.wikipedia.org/wiki/Quaternary_ammonium_cation

Title: Re: How does soap make us more clean than just water does?
Post by: apratact0 on 02/08/2018 01:19:01

Thats what I was wondering.   We are essentially washing away the oils on our hands.   So the germs and bacteria are basically clinging on to these oils.   then washing with soap thus would help wash away germs, bacteria, dirt, oils, etc..

Title: Re: How does soap make us more clean than just water does?
Post by: chris on 02/08/2018 17:05:07

Quote from: apratact0 on 02/08/2018 01:19:01

Thats what I was wondering.   We are essentially washing away the oils on our hands.   So the germs and bacteria are basically clinging on to these oils.   then washing with soap thus would help wash away germs, bacteria, dirt, oils, etc..

Sort of; the rubbing action of the hands against each other beneath running water is what actually does most of the dislodging of skin microbes. The soap helps to lever up dirt, oils and debris that might help to glue them in place.

In tests, almost nothing beats soap and water in infection control tests in hospitals.