The funny little thing that is Cetearyl Alcohol

If you’ve ever tried making a cosmetic cream before you’ll no doubt have noticed that cetearyl alcohol can make it super thick.  If, like me, you’ve wondered how it manages to do such a thing so efficiently, you might well have googled it.  I googled it once and was somewhat meh about the explanations that were forthcoming but that’s what you get when you just google, mostly rubbish.  What we need to do my fine people of the inter webs is ‘Google Scholar’ it or, as I prefer, delve into the DeepDyvve archives….

So of course, you can’t make creams for 20 years without knowing a bit about this ingredient and I sure did but the exact chemistry of it had been something that didn’t command my full attention until now, mainly because it wasn’t particularly necessary until now, a time when I’m getting more and more stuck into complex emulsions, high levels of actives – especially salty things and formulating for top-level results. These types of formula can be pretty dam twitchy and so knowing your chemistry inside-out sure does help. So let’s have a look.

Cetearyl Alcohol is a fatty alcohol. 

Cetearyl = Cetyl + Stearyl.

Cetyl = C16,  Stearyl = C18

Back in the 1960’s there were a few studies done on the effect of fatty alcohols on emulsion stability and it was found that the blend of cetyl and stearyl were the best for the job.  If you are buying ingredients for making creams do keep in mind that cetearyl alcohol is a blend of two alcohols and the ratio can vary between suppliers so your emulsion results might vary if/ when you change material sources.

For those palm free lovers out there this ingredient can be made from petroleum derivatives or natural sources.  Up to the time of writing I’ve not managed to source a single batch of palm free cetearyl alcohol although I know it must exist as there is a company in Italy, Kalichem, making emulsifiers that are palm free and contain this.  So, at present, most palm free emulsions that are also natural are sans cetearyl alcohol unless it comes from Kalichem in the form of a blend.  If you are reading this in the future, this point may have become irrelevant.

Being a fatty alcohol this beast isn’t soluble in water.  The thing holding this dude back from water solubility is that big old carbon tail at 16 carbons long.  Saturated carbon chains are non-polar and as water is polar and as like-dissolves-like this thing ‘ain’t playing.   So expect to find your cetearyl alcohol as a waxy solid that gets mixed in with your oil phase and melted prior to emulsification.

Cetearyl Alcohol in an emulsion.

A simple cosmetic emulsion is usually some oil droplets stabilised (at least to a degree) in water to form a homogenous mixture that looks milky or creamy.  Cosmetic emulsions look milky or creamy because the inner phase is bulky and light can’t pass through it. This is partly because the inner phase is usually quite big in terms of volume (5-40%) but also because cosmetic emulsifiers generally form relatively chunky internal phases (well, chunky when compared to micro emulsions) because of their chemistry and how the congregate around the oil droplets.  In any case the thing you make looks opaque most of the time.

So where does the cetearyl alcohol sit in an emulsion?

You could be forgiven for thinking that cetearyl alcohol just adds ‘waxy’ bulk to the internal oil phase as it is a waxy, oil soluble material after all and that the act of making the internal phase harder will thicken the cream.  While that theory has some merit  if that was how cetearyl alcohol worked it would be pretty damn impressive to change the cream viscosity as much as it does.

I figured this out a while ago by doing some experiments with cetearyl alcohol vs other waxes and butters. It didn’t take long to realise that there was something going on with the water phase for an ingredient to make THAT much difference.  I knew back then it had something to do with the -OH part of the cetearyl alcohol and I knew that liquid crystals were involved but it’s only now that I’ve really got my head (and reading) around what’s actually going on.

Cetearyl Alcohol – queen of the liquid crystal network!

Liquid crystals are structures that fit between…. wait for it…. liquid structures and crystal structures.  Helpful?  I thought not.

So a crystal structure is usually some sort of rigid lattice where molecules interact in a highly ordered and rigid form – like a Jenga puzzle I guess you could say.   On the other end of the scale are liquids which are pretty chaotic and messy – rather like my office on a normal day.  A liquid crystal fits in the middle being structured yet fluid – like magic.  Basically you usually end up with layers of structure that can move over each other to some degree like fluid so you get a nice flowing structure.  This structure has been found to give superior moisturisation to a cream as the liquid crystal layers trap moisture in between them thus increasing the potential for the cream to hydrate the skin.  These structures are usually more stable than a classic oil-in-water emulsion and are more likely to act as skin delivery systems due to the way the cream is orientated – sheets of water and /or oil can be deposited as opposed to just drops.

So Cetearyl alcohol helps build these but how?

This is the bit I hadn’t really got a handle on until now but now I can show you (I think).

So, Cetearyl Alcohol likes to hang around like a moving snake, a bit wibbly but not curled up (some structures online show it bent, it usually isn’t, there is no need for it to be anyhow as the influence of it’s OH group wouldn’t be able to bend it very much).    I’ve drawn it at the top there,  lots of carbons and hydrogens in a slight zig-zag formation with an OH group at one end.  The OH group of the Cetearyl Alcohol (I’ve drawn the cetyl chain here) is the part where all the action happens, the fun end of the molecule.  OH is polar and water-loving so it will be attracted to water and/or the cream emulsifier which has to have some kind of action centre to be useful as an emulsifier – either non-ionic or ionic it doesn’t matter.

To get cetearyl alcohol to work well one needs a slight excess of emulsifier – that is, slightly more emulsifier than you need to emulsify your cream.  If you are trying to work out how to know how much that is you could do this.  Make your cream without cetearyl alcohol then run what I call ‘boot camp’ stability on your emulsion – 5 x freeze/ thaw plus centrifuge @ 5000 RPM for 15 minutes.  If it survives that you have enough and you might want to half the level and keep doing that until you find the sweet spot of ‘a bit too much but not way too much’.  The excess emulsifier floats around in the water phase as micelles (little gangs of free emulsifier).  Have too much and you destabilise your cream out the other end as these micelles will compete with your true emulsion for water and your cream will dehydrate which could look waxy or could look just totally unstable.

So you have a little emulsifier floating in the water which is great, now add some cetearyl alcohol – maybe start with 0.5% then try a bit more and more until you again reach that sweet spot.  Too much cetearyl alcohol and your nice thick but pliable cream will turn waxy – I’ve done that a few times hence me re-visiting my notes on this and applying a bit more thought.

Now you have a little cetearyl alcohol and a little excess emulsifier in the water the action can begin.  What happens next is a dance between these two things.   Apparently the best interactions occur when the emulsifier has a similar tail group to the cetearyl alcohol.  That’s probably why lots of emulsifiers are ‘cetearyl’ based…..

Basically these things join together in sheets (technically speaking a gel phase is created), hand-in-hand forming layer after layer of fatty chains and -OH group heads – the technical term for the rheology of this is a viscoelastic network.  The emulsifier will have more ‘surface-activity’ or pulling power than the cetearyl alcohol so it will most likely lead the dance if you will.

In between these sheets traditionally dispersed oil droplets become trapped (happily so) and alongside those is the continuous phase, water.  This water lubricates the sheets allowing them to pass over each other but they don’t completely float away because of the -OH bond anchors at the ends of the cetearyl alcohol and emulsifier.  This beautiful structure brings both viscosity and stability if the correct balance is reached.

So what can kill the cetearyl alcohol thickening party?

Well as I mentioned in the beginning, I’ve been working on more active and more salty creams of late and that’s what has caused me to go back and revisit cetearyl alcohol.  Salt of any kind sits in the water of an emulsion and there it exerts its effect, making the water more active (rather than passive) and increasing the conductivity of the emulsion (the amount of electrical current that can pass through it).  We know from various scientific studies that an increase in emulsion conductivity spells a decrease in emulsion stability and so this can be bad news.  Cetearyl alcohols ability to form these interactions with the excess emulsifier are disrupted by salt as the salt competes with the excess emulsifier for bonds.  At low levels this may just manifest in a slight loss of viscosity but as the saltiness increases the thickening you gained from adding cetearyl alcohol is all but lost and its addition becomes almost pointless.  No amount of cetearyl alcohol will help rectify the viscosity drop in a high salt environment as it isn’t the amount of cetearyl alcohol that’s important here, it’s the environment required for bonds to form (it’s like a door has closed on it) and as adding more cetearyl alcohol doesn’t change its chemistry it does nothing more than just waste more material in applying an ineffective fix.

I’m still experimenting with this in emulsion settings but so far it doesn’t so much look like you can’t use cetearyl alcohol in a salty emulsion at all but more like it may not perform as well as you were expecting and may even be almost useless as a thickener in very salty emulsions.   Now I’ve managed to make some very strong emulsions with magnesium salts using emulsifiers like cetearyl alcohol and cetearyl glucoside as a pre-made blend but I’m now inclined to think that the cetearyl alcohol component of the blend is doing nothing much and that it is all thanks to the cetearyl glucoside  that we have an emulsion – so basically I’m wasting my money having the cetearyl alcohol in there.

And what about other things, is there anything else that can do this or is it just cetearyl alcohol?

Any fatty ingredient you add to your emulsion that has some degree of polarity or -OH functionality can form interactions with the water phase and as such may not sit completely within the dispersed oil droplet.   This interesting experiment looked at how adding different fatty esters affect the stability and formation of liquid crystal structures.  Many chemists add things that are amphiphilic to their emulsions, things such as Isopropyl Myristate, Cetyl Palmitate or even Stearic Acid and these could all play a part at that interface.  As I mentioned other fatty alcohols have been looked into as well but the shorter chain fatty alcohols were not as good at stabilising the emulsion or thickening it as cetearyl alcohol was found to be.

So is there anything else we need to know about Cetearyl Alcohol before we go?

Well yes, I think there is.  If you have had the good fortune to have played with this ingredient before you might have noticed that it does take a while for the cream to fully thicken when using cetearyl alcohol as a thickener.  This is because it takes time (and a change in temperature) for this gel-phase liquid crystal structure to form.  To fully orientate the molecules into these sheets can take up to 24 hours and requires the cream temperature to drop to at least room temperature.  Where things sit and line up in an emulsion are influenced by a few things – saltiness we’ve mentioned here but also pH and temperature.  So many things to keep your eye on and test – that’s why stability testing happens over different temperatures and why we take note of pH and water loss over time.

Cetearyl Alcohol has, for me, been one of those sneaky little ingredients that I’ve taken for granted in my formulating up to now but as my formulating work has morphed so too has my understanding of this quiet little achiever.  Used correctly it can transform a simple cream into a multi-dimensional active delivery system.  Used willy nilly it can turn your cream into a waxy mess (and yes, I’ve had more than my fair share of those).

I hope this has helped you understand this fascinating ingredient a little better and ultimately helps you formulate more effective products.

Amanda x