Are Lauric and Myristic acids still drying in liquid soap?

[DeeAnna]

...If the shorter chain fatty acids contribute to the more aggresive cleansing action, why are they not considered in any soapmaking calculator? ...

I can't answer that -- you'd have to ask the calc developers about that, not me.

Maybe because the fatty acids ignored by the soap recipe calculators are only found in just a few fats?

Maybe because the % of these fatty acids is usually very small in a blend of fats typically used for soap making?

Maybe because small-scale soap makers don't know certain fatty acids can affect the degree of irritancy to the skin, so they're not aware they should be aware of this issue?

All I know for certain is even the oldest online calc I know of -- the now defunct SummerBeeMeadow -- only tracked the "big 8" fatty acids. Soapcalc is the next oldest calc I know of and it does likewise.

...And what is it that causes this ability to remove oils so effectively in these short(er) fatty acids? Does their carbon tail length or structure influence this ability?...

Fatty acids vary based on the number of carbon atoms in their structure, so, yes, the "carbon tail length" is the reason why some fatty acids are considered to be "shorter" and some "longer." The other issue is the degree of saturation of the fatty acid -- in other words the number of double-bonds, if any, in that carbon chain. A fully saturated fatty acid has no double bonds.

Sounds like you might want to look at dermatological studies that evaluate the degree of skin irritation caused by various cleansers and why the irritancy varies. You might start with "Correlation between pH and irritant effect of cleansers marketed for dry skin" by L. Baranda and others. It's available for free on the 'net.

 

[Sri Astuti]

I can't answer that -- you'd have to ask the calc developers about that, not me.

Maybe because the fatty acids ignored by the soap recipe calculators are only found in just a few fats?

Maybe because the % of these fatty acids is usually very small in a blend of fats typically used for soap making?

Maybe because small-scale soap makers don't know certain fatty acids can affect the degree of irritancy to the skin, so they're not aware they should be aware of this issue?

All I know for certain is even the oldest online calc I know of -- the now defunct SummerBeeMeadow -- only tracked the "big 8" fatty acids. Soapcalc is the next oldest calc I know of and it does likewise.



Fatty acids vary based on the number of carbon atoms in their structure, so, yes, the "carbon tail length" is the reason why some fatty acids are considered to be "shorter" and some "longer." The other issue is the degree of saturation of the fatty acid -- in other words the number of double-bonds, if any, in that carbon chain. A fully saturated fatty acid has no double bonds.

Sounds like you might want to look at dermatological studies that evaluate the degree of skin irritation caused by various cleansers and why the irritancy varies. You might start with "Correlation between pH and irritant effect of cleansers marketed for dry skin" by L. Baranda and others. It's available for free on the 'net.

OMG. I love you so much, @DeeAnna ... You are just brilliant.

Yes, I've been reading some dermatological studies, too, and one that I have found (Effect of Alkyl Structure and Saturation of Fatty Acid Sodium Soap on Skin Barrier Function, by Kubota et al., also available free on the net) confirmed that Sodium Laurate did do quite a serious morphological damage to the skin more than other soaps, with Sodium Stearate as "the gentlest", so to speak. Or so I understand. Mind you, English is not my mother tongue.

And being a non scientist, I cannot imagine how that can happen. In my layman's mind, I am imagining that the smaller the size of the molecules mean they can penetrate better into the intercellular lipid matrix of the stratum corneum and do damage by lifting the lipids. Sodium Stearate molecules, being the longest and the straightest, cannot do this easily, so they don't do much damage to the skin barrier. But this is just me thinking hahahaah.

You are welcome to set me straight with all your scientific knowledge and expertise.

 

[DeeAnna]

...Sodium Laurate did do quite a serious morphological damage to the skin more than other soaps, with Sodium Stearate as "the gentlest", so to speak...

Yep, that's my understanding too. The shorter the carbon chain, the harsher the cleanser -- more irritating, stripping, and drying. That's especially true when you get down to lauric with 12 carbon atoms (C:12) and shorter. I've mentioned butyric C:4, capric C:10, and caprylic C:8 fatty acids -- you can see they're even shorter than lauric acid.

Another aspect to consider is the water solubility of the soap. A soap that is more soluble in water, all other things being equal, might be more irritating to the skin than the same soap that's less soluble. Example might be soap made with NaOH (less soluble) compared with the same soap made with KOH (more soluble).

I've wondered if the higher solubility of olive oil soap is possibly why some people find olive oil soap to be drying to their skin, despite the common wisdom that it's one of the milder soaps one can use.

 

[Sri Astuti]

Another aspect to consider is the water solubility of the soap. A soap that is more soluble in water, all other things being equal, might be more irritating to the skin than the same soap that's less soluble. Example might be soap made with NaOH (less soluble) compared with the same soap made with KOH (more soluble).

I've wondered if the higher solubility of olive oil soap is possibly why some people find olive oil soap to be drying to their skin, despite the common wisdom that it's one of the milder soaps one can use.

Is this because the more soluble the soap is, the more soap molecules that are released to clean our skin? So they have the bigger potential of lifting/stripping more of our skin natural oil??

 

[DeeAnna]

Is this because the more soluble the soap is, the more soap molecules that are released to clean our skin? So they have the bigger potential of lifting/stripping more of our skin natural oil??

Basically yes.