Thursday, April 8, 2010

Surfactants: Alkyl sulfates

Alkyl sulfates are probably the most maligned of the surfactants. They are organic esters of sulfuric acid created by sulfation of a fatty alcohol chain that vary according to the number of carbons in that hydrocarbon chain. (For instance, if you were sulfating lauric acid, you'd have a carbon chain of 12 carbons. If you were sulfating oleic acid, you'd have a carbon chain of 18 carbons, and so on.)

They are good foamers in hard water, but the best foam comes from those fatty acids in the C12 to C14 range (so lauric or myristic acid).

Sodium lauryl sulfate is in this category. (It has 12 carbons, so we know it comes from lauric acid). It very poorly tolerated by our skin - is is considered not so mild - and the irritation potential is quite high when compared to just about every other surfactant! It is normally used in combination with other, milder surfactants to make it less irritating to our skin. It is very easy to thicken SLS with salt, but you can use Crothix or glycol distearate (EZ Pearl) as well (and both of these are good moisturizers for your skin, so they will reduce the irritation potential).

You can find the lauryl sulfates with ammonium and magnesium ions as well. Of all the sulfates, ammonium is the least irritating, then sodium, then magnesium.

It is a great foamer and can boost the foam capability of other surfactants greatly.

As a disclaimer: I have never used SLS in any of my products, so I can't give you any formulation ideas. It's not because of the things we hear about them, but because I wasn't able to find it initially. I still don't use it because there are so many other less irritating surfactants than SLS.

SLS is used in many commercial formulations because it is inexpensive, offers great foaming, and can be thickened easily with salt. Something like Stepan's version of SLS (data bulletin here) is 29% active, and 10% can cause mild to moderate skin irritation. So using 35% or so of SLS in a product could cause skin irritation.

Please do not post a bunch of comments about how bad SLS is for you, how it can give you cancer, and how it is used to clean garage floors. I think we've established that it's not a great surfactant choice because of the high irritation potential. If you wish to leave a comment of this nature, please give me some links to studies that back your position that aren't from the EWG or Skin Deep sites. For more information about the myths of SLS, please visit - it's a great site!

Join me tomorrow for fun with alkyl ether sulfates like SLeS!


Apryl said...

Thanks for the info on SLS. I also checked out the site you mentioned. Interesting. I've recently decided that we should cut out some of the unnecessary products in our home (ex. if I can use a body butter-shea butter, oil, glycerine-on my son's severely dry skin that works better than a commercial lotion, why not?) and I'm finding that going completely "natural" is not really an option. Your site is super informative and I'm so excited to start trying some of your recipes! It's amazing to find a source of practical information online that is backed by science and fact rather than hearsay. . .

Susan Barclay-Nichols said...

Hi Apryl. I think we all start out wanting to make all natural products, but research shows us how impossible 100% can be if we want to make oil-in-water products. The holy grail is all natural preservative, but if it were possible, the big and medium sized companies would be doing it by now. I think we find out what we love, what we can live with, and what we can't live with and make our choices accordingly.

I don't call things natural; I call them minimally processed, because everything we use is processed in some way. If we had raw honey, it could be full of bee parts! If we had raw olive oil, it would be olives we'd have to squish ourselves! You can take the word natural the other way - every ingredient that contains a hydrocarbon is "organic" in the sense of organic chemistry, so when I see something like BTMS described as organic, it might be make go "argh!" but it is technically correct.

Tara said...

Does sodium coco-sulfate fit into this category? I bought some from another formulator (who bought it from The Herbarie), and now I have no idea how do formulate with it. Maybe I will make a shower gel for my husband, since he doesn't experience irritation the way I do.

Tom Jensen said...

Hi Susan,
I know that Orvus is a paste or liquid and dreft is the spray dried version. But, are they both alkyl sulfates or is the spray dried version the alkyl sulfate?

Susan Barclay-Nichols said...

I'm sorry, Tom, but I'm afraid I have no idea what Orvus is. Could you please send me a few links to this product so I can look into it?

firegirl said...

Hi Susan,

Why is the ability to foam well seen as a important advantage when it comes to SLS and other surfactants. I like bubbles in my bubble bath but is there any practical advantage that goes beyond my somewhat childish enjoyment of sitting in a mountain of bubbles. Is there any point of having them in products like washing up liquid?

Thanks a lot