# Is it known for sure that bases feel slippery because of the production of soap/surfactant?

Discussion around the question Why does bleach feel slippery? has started me thinking about the saponification explanation for the slippery feeling of basic solutions.

According to Wikipedia:

Alkaline drain openers can dissolve hair (containing proteins) and fats inside pipes via alkaline hydrolysis of amide and ester respectively:

$$\ce{RCONH2(amide or proteins)+ OH− → NH3 + RCOO−}$$

$$\ce{RCO2R’(ester or fats)+ OH− → R'OH + RCOO−}$$

and just above that:

Essentially, the hydroxide ions from the basic lye attack the carbonyl carbons of the fat, which eventually kicks off the hydrophobic tails of the triglyceride (tristearin/fat) to isolate glycerol.

So I am not sure if the "saponification" explanation for why a small amount of a fairly strong base feels slippery between thumb and forefinger really says that the reaction has produced a true soapy surfactant or that it should really say that it is lubrication by glycerol-like compounds that generate the intense slippery feeling.

Wikipedia also says:

The Stratum corneum (Latin for 'horny layer') is the outermost layer of the epidermis, consisting of dead cells (corneocytes). This layer is composed of 15–20 layers of flattened cells with no nuclei and cell organelles. Their cytoplasm shows filamentous keratin. These corneocytes are embedded in a lipid matrix composed of ceramides, cholesterol, and fatty acids. (emphasis added)

Corneocytes are keratinocytes and named as such because of the abundance of keratin protein filaments they contain.

I seem to remember my very smart high school chemistry teacher telling us that the breakdown of protein was also important, but I don't remember the production of soap as being so central. So I'd like to ask if there is any actual empirical evidence - ideally with a scientific reference, that demonstrates which molecules present between the fingers in this situation is primarily responsible for the slippery feeling. Potential candidates might include:

1. Soap/surfactant,
2. Glycerol produced from hydrolysis of "finger lipids",
3. Broken down protein products, or
4. the pre-existing inter-cellular lipid layers that would be exposed by the removal of successive layers of cells within the stratum corneum.

below: Epidermal layers, from here.

"Slippery" is vaque. When dealing with 0.5 to 5 M NaOH and gloves I had not really the impression it was slippery by itself. For sure the solution becomes slightly more viscous at higher molarity. Similiar to making a higher molarity Urea solution. If at all the soap like effect is weak.

• Wearing gloves makes your answer moot. "So I am not sure if the 'saponification' explanation for why a small amount of a fairly strong base feels slippery between thumb and forefinger really says that the reaction has produced a true soapy surfactant or that it should really say that it is lubrication by glycerol-like compounds that generate the intense slippery feeling." Note also the proteins and lipids tags, and the large image of Epidermal layers. – uhoh Nov 15 '18 at 10:25
• on skin, I also had not really the impression it is soapy. maybe you should wait until it dissolves your layers :D But then it is because of the dissolved keratin and not NaOH :/ – dgrat Nov 15 '18 at 10:27
• I hope you haven't put several Molar NaOH solutions on your skin, nor anyone else's. Chemistry SE may actually have some rules about discussing dangerous activities in posts or comments. Here I'm just quoting Wikipedia and my beloved high school chemistry teacher. – uhoh Nov 15 '18 at 10:29

Potential candidates might include:

1. Soap/surfactant,
2. Glycerol produced from hydrolysis of "finger lipids",
3. Broken down protein products, or
4. the pre-existing [inter-cellular lipid layers][5] that would be exposed by the removal of successive layers of cells within the stratum corneum.

Very good guesses but none of the above actually (i think, what does "finger lipids" mean?). But the reason bases feel slippery to bare skin no matter how much you scrub first, is bases attack the phospholipid bilayer of your cells quite readily not only saponifying them, but breaking the inter-molecular bonds of molecules that already resemble a soap. Take for example phosphatidylcholine:

The phosphochloline already has all of the elements to make a soap and when base is added, the molecule does not need to interact with other molecules to achieve local charge balance, but now have the ions from the base to balance, which breaks intermolecular bonding creating a small layer of soap, making the base feel slippery.

• I see; bases allow us to "release our inner soap". This is a very helpful and teaching answer, thank you very much! – uhoh Nov 16 '18 at 0:31

• Re: Also, your first Wikipedia link claims $\ce{OH-}$ "reoxidizes" $\ce{Al2O3}$. That is ludicrous. // Actually that is exactly how it works... All Al metal has a coating of $\ce{Al2O3}$. – MaxW Mar 14 '17 at 17:04