All SCI contains some fatty acids that are left over from the coconut fatty acids used to create them. Some have more, some have less, but they all have a bit of fatty acid left in the process. This fatty acid helps increase mildness in our products and might be a reason that it feels so lovely on our skin. Are these fatty acids stearic acid? Possibly. Coconut oil doesn't contain a lot of stearic acid - it's mostly lauric acid, which has a great affinity for hair, and myristic acid, with a titch of the other acids thrown in for fun! - but we could find any of the fatty acids found in coconut in the end product of SCI.
Some SCI has an INCI of sodium cocoyl isethionate and some has an INCI of sodium cocoyl isethionate (and) stearic acid. This means stearic acid has been added to the mix to make it more noodle-y or flake-y. But all SCI contains some free fatty acids in the mix left over from the process of turning coconut oil into a surfactant.
For instance, Jordapon CI prill contains less than 6% fatty acids (INCI sodium cocoyl isethionate). Geropon by Rhodia contains 60% actives, less than 10% coconut acid, and more than 25% stearic acid (INCI sodium cocoyl isethionate (and) stearic acid). Tauranot 1-78 contains 10% to 12% free fatty acids and is 80% to 82% active (INCI sodium cocoyl isethionate). And Elfan by Azko Nobel has 7% to 12% free fatty acids with 81% to 86% actives (INCI sodium cocoyl isethionate).
It seems that some people have the idea that having stearic acid in our SCI isn't a good thing. Like everything in life, it depends upon the application (chocolate good in my mouth, not so good in my purse on a hot summer day). In my personal experience - and I recognize that the plural of anecdote isn't data - SCI with stearic acid in the INCI name doesn't agree with my oily hair when I put it into shampoo bars or liquid shampoo, but it's absolutely wonderful in body washes, facial cleansers, and other applications because it adds that wonderful creamy lather and lots of thickening to the product. So if you were to ask me if I thought SCI with stearic acid was a bad thing, I'd say no! It's great! But it doesn't work well for me in a shampoo for very oily hair.
In the interest of complete disclosure, I am writing this post because I received a phone call from Angie at the Herbarie. She has been asked the question about the SCI with stearic acid a number of times and was worried that I was saying that SCI with stearic was bad and wanted me to clarify this on the blog. SCI with stearic acid is not a bad thing. It's a very creamy feeling product with emolliency that will help thicken your products if you're making liquid surfactant mixes. And yes, all forms of SCI will have free fatty acids in them and the amounts differ depending on the manufacturer and the addition of extra stearic acid. Please stop asking her about her SCI!
I hope I've clarified this!
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