Emulsifiers

When we think of emulsifiers in product formulations, we often assume that they only serve a functional role and don’t really associate them with any skin benefits. But they actually do so much more. As functional ingredients, emulsifiers are the powerhouse of two-phase (or even multi-phase) products like creams, and without them we’d end up with a ton of shake-well products. They are surface-active ingredients which lower the surface tension of a dispersed phase (e.g. oil) so that it can be combined into an immiscible continuous phase (e.g. water) and a homogeneous product can be obtained. Emulsifiers also dictate the texture of a product, specifically impacting the appearance and skin-feel during the early phases of application. Through our research and studies we found that they have an influence on the rate of barrier repair too, which can be attributed to the structures they form and their interactions with the intercellular lipids of the stratum corneum. Therefore, when selecting an emulsifier system for C.R.E.A.M. 2.0 there were three criteria which we considered:

• stability
• texture
• barrier repair ability 

Stability

You know how they say not to cry over spilled milk? Well, we cried over a lot of split creams. Barrier lipids, especially ceramides, are extremely difficult raw materials to work with and not every emulsifier system is compatible with them. Since ceramides are nearly insoluble at room temperature, they must be added to the oil phase of an emulsion (which also contains the emulsifier) and heated to 90°C. Interestingly, we observed that when only the emulsifier was changed in the formulation there was an impact on the solubility of ceramides. With some emulsifiers, no matter how long or how high we heated the oil phase, the ceramides would just not solubilize. We also found that not every emulsifier can handle a high load of actives and our 10-ingredient soothing complex could not be mixed in. However, these weren’t even the worst parts of the development process. Once we had what appeared to be stable emulsions, we stress tested them at 40°C and, thus, the waiting game began to see if they would remain intact or if we would just end up with another broken cream. 

Texture

Of the stable formulations, we then looked at texture. Although texture preference is very subjective, we often got a lot of comments on the spreadability and final skin-feel of our first version of C.R.E.A.M., so we knew we wanted to improve on these. In our C.R.E.A.M. 2.0 pre-survey results, the majority of our R&D product testers said they prefer a texture between rich and light (45.1%), followed by a preference for rich and substantive (31.4%). We were really happy to see these results because it aligned with our thinking that a barrier cream should be a substantive product. With this in mind, we then evaluated our stable formulations, looking for a formula that was on the thicker side but did not feel too heavy on the skin. 84% of differences in emulsions are observed in the early phases of application, specifically the appearance, pickup and rub-out; with 74% of the variance being attributed to the emulsifier [1]. We managed to narrow it down to the following three emulsion systems that gave us our desired texture:

• CrystalCast MM: Beta-Sitosterol (and) Sucrose Stearate (and) Sucrose Distearate (and) Cetyl Alcohol (and) Isostearyl Alcohol
• Montanov 202 + Montanov 68: Arachidyl Alcohol (and) Behenyl Alcohol (and) Arachidyl Glucoside + Cetearyl Alcohol (and) Cetearyl Glucoside
• Olivem 1000: Cetearyl Olivate (and) Sorbitan Olivate       

Barrier Repair Ability

Although all the emulsifiers form crystal lamellar emulsions which reinforce the skin barrier, we decided to test them for their barrier repair abilities. What surprised us is that the emulsifier’s effect on trans-epidermal water loss is paramount! We expected all formulations to perform similarly as the only difference was the emulsifier, but we observed that the rate of barrier repair was substantially altered just by changing one variable. After the 2 hour mark, Montanov 202 + 68 accelerated barrier repair more than the other two formulations, achieving 90% repair in just 6 hours. At 8 hours, Montanov 202 + 68 achieved 93% barrier repair, while CrystalCast MM and Olivem 1000 achieved 88% and 83% repair, respectively. Since Montanov 202 + 68 was the only emulsifier that was able to achieve over 90% barrier repair and met all our other criteria, it was the blend which we selected to use in C.R.E.A.M. 2.0.

Takeaway

So it seems like seemingly inert ingredients, like emulsifiers, do actually have an influence on barrier repair. Even though all of our test formulations contained the 3:1:1:1 barrier lipid ratio, by changing one functional ingredient the formulation’s ability to accelerate barrier repair through TEWL reduction was affected. This means that all the ingredients in a barrier repair formula need to be carefully considered, not just the actives. It also shows us that we don’t know how a product affects the skin barrier until we test it. 

References