Dear Valerie: I read that Potassium Cetyl Phosphate can replace water-phase gelling agents. Do you know the inner workings of the emulsifier and how exactly does it function in an emulsion? 

—Stability Issues

Dear: Stability:

Potassium Cetyl Phosphate (PCP) is an oldie, but goodie, emulsifier. How oldie? I’ve seen documents on this material dating back to the early 2000s, but its grandfather, DEA-Cetyl Phosphate, upon which it is based, is about 80 years older. DEA-Cetyl Phosphate is not really favored in cosmetics anymore due to the DEA portion of the molecule. In case you aren’t aware, DEA is listed on California’s Proposition 65 as a secondary amine. There is concern it may form nitrosamines (which are known to the state of California to cause cancer). The daddy of PCP, Cetyl Phosphate, is still often used in cosmetics, but it’s not as popular as PCP. Cetyl Phosphate works similarly but requires neutralization. Compounding doesn’t like extra steps (who does?) so PCP, which does not require neutralization, is the primary “cetyl phosphate” used in cosmetics.¹

I must be honest; I often forget about PCP. But when I use it, I marvel at its aesthetic qualities as if I’m seeing it for the first time and want to hit myself in the head for ever even forgetting about it! The resulting creams are lightweight yet have a pleasing, luxurious texture. The cetyl moiety has quite a compatible skin feel, offering that extra sense of skin quenching one desires in a cream. It’s really a no brainer to consider using, and its versatility means options!

When It Comes to PCP Think UV Protection!

Where PCP really shines is its stalwart ability to act as a primary, anionic, oil-in-water emulsifier with high quantities of polar and non-polar oil phases. Think sunscreens! Its resulting emulsions are not only elegant, but quite stable. Its stability is rendered by its ability to form both liquid crystals and multi-lamellar structures, not micelles, during emulsification. The liquid crystals essentially look like oil-containing vesicles with polar heads that form the vesicle membrane. Except, in the case of PCP, portions of the polar heads are negatively charged. When two liquid crystal vesicles approach each other, instead of converging, they are repulsed, thanks to the negative charges. This unique property of PCP affords it superior stabilization properties, even at elevated temperatures.

It’s in this sense that PCP forms a gel network to stabilize emulsions. PCP doesn’t really take place of traditional water-gelling agents. Those agents function through polymeric structure to immobilize the oil in the dispersed phase, slowing down their coalescence. PCP offers pleasing haptics to any cream but doesn’t necessarily offer the same tactile or user experience in pick up or break upon application to skin. There is still a place for water-gelling agents in formulas with PCP, but they’re not necessarily needed for stability if PCP is properly formulated. In fact, I encourage the use of water-gellers!

PCP Doesn’t Need a Starring Role

PCP doesn’t always need to take center stage. It can act as an understudy (at just 0.25-0.5%), supporting other primary emulsifier when a little extra stabilization is needed. At this low use level, it still forms “anionic micro domains” to stabilize emulsion droplets, practically freezing them in their place.

The viscosity result with PCP can be tailored by selecting the right emulsifier for your viscosity and [furthermore] using it at the optimum ratio. For example, you can generate great viscosity response with just PCP and cetearyl alcohol at a 1:2.3 ratio. Want to lower viscosity? Reduce overall use levels, alter the ratio or swap out the fatty alcohol with another co-emulsifier. Play around!

Keep in mind PCP can be processed in the water or oil phase—preferentially the latter. It doesn’t dissolve regardless of which you choose, so you must trust the process when you dump your turbid oil phase in the main vessel at a steamy 85-90ºC with rapid mixing. Be sure not to leave any PCP behind! Your final product pH should be 5-8, although most emulsions with PCP tend to naturally hit 5-6. Another reason to love PCP, you don’t necessarily need to adjust pH! Lastly, PCP emulsions do need time for its crystalline structure to form; final viscosity arrives in 24-48 hours.

Valerie George

askvalerie@icloud.com

Valerie George is a cosmetic chemist, science communicator, educator, leader, and avid proponent of transparency in the beauty industry. She works on the latest research in hair color and hair care at her company, Simply Formulas, and is the co-host of The Beauty Brains podcast. You can find her on Instagram at @cosmetic_chemist or showcasing her favorite ingredients to small brands and home formulators at simply-ingredients.com