Dear Valerie: Thanks for answering my previous question in October on whether or not glyceryl oleate can build viscosity in APG-based bodywashes. This led me to another question—can you increase the viscosity of a surfactant system based totally on alkyl polyglucosides?
—THINKING MORE CLEARLY

Dear Thinking:
I am glad my previous answer was of help to you. I’m afraid the news here, though, doesn’t look as good. As APGs are nonionic, they are extremely difficult to thicken when not used in coordination with anionic and/or amphoteric co-surfactants. APGs are just unresponsive on their own.

The easiest way to increase viscosity in a completely nonionic, APG-based system would be to incorporate thickeners into the water phase. I would start with carbomer-type thickeners, but I suspect if you want to only use APGs this may not fit into your formulation values. You will get some thickening with hydroxypropyl methylcellulose or xanthan gum, but I don’t believe it will be substantial or yield good long-term stability.

If you’re formulating with multiple types of APGs, like lauryl, decyl and coco glucoside, make sure you play with the ratios to each other to see if increasing one over the other impacts final viscosity—it just might. Hopefully, this helps you crack the viscosity code!


Dear Valerie: I have been tasked with formulating a waterless facial cleanser based solely on sodium cocoyl isethionate. Is it possible to take pure SCI powder and use it as the entire formula?
—TAKE A POWDER

Dear Take:
It’s an interesting approach and I appreciate the simplicity, but there are a few concerns in doing this. Even the largest pieces of SCI co-exist with extremely fine particulate powder that volatilizes in the air, becoming a health hazard. In fact, when looking at the SDS—which would apply to a 100% formulation of the neat material—it recommends wearing PPE during handling to avoid inhalation. If you’ve ever worked with this raw material, you know that it is not fun to breathe in. This provides a huge safety risk for consumers.

The other concern with this approach is that the Cosmetic Ingredient Review (CIR) Panel has recommended the maximum use level of SCI be restricted to 50% in rinse-off products and 17% in leave-on products. Using only SCI at 100% in a face wash is double the recommended safety limit. I recommend reading the full report to also see data on irritation with this surfactant.

Lastly, I would imagine using only SCI is not a pleasurable experience. It has incredibly low water solubility so you may need other ingredients to help cover up the fact that it’s not going to solubilize well in the palm of your hand.


Dear Valerie: I’ve been trying alternative preservation systems and made a lotion with gluconolactone (and) sodium benzoate. After two weeks, the pH dropped from around 4.5 to 4.0. I’ve narrowed it down to the preservative being the issue. How do I stabilize it?
—SEEKING STABILITY

Dear Seeking:
I’m surprised the pH isn’t dropping further—it just might. The situation you’re currently in is notorious for this preservation system and like many others, I’ve been in your shoes. Gluconolactone is hydrolyzing over time to gluconic acid. This lowers the pH of your formula. It’s somewhat easily correctable by formulating with a buffer system or by following the manufacturer’s instructions for self-buffering the preservative.

To self-buffer this preservative, combine it in a side kettle with water that is withheld from the main batch. The manufacturer recommends 10-15% of your water phase. Note the side kettle is probably more like a side tank! Once dissolved, add an alkali like sodium hydroxide until the pH of the pre-mixture is above 7.5. It needs to stay above 7 for 30 minutes, or else you need to add more alkali, so prepare to do this around lunchtime. Once the pH is stable, transfer the pre-mixture to your main kettle with the rest of the ingredients and continue your batch. Adjust the final batch to a lower pH using citric acid. Your system is now buffered.

Alternatively, you can conduct this in one kettle by adding the preservative to your main vessel under heat (50ºC) and take the entire system up to a pH of 7.5 with your favorite alkali. If the pH holds above 7 for 30 minutes, you can lower it using citric acid. If you’ve already taken lunch, consider filing some paperwork to clear up your desk.

If this seems like a lot of work, it’s because it is. I wouldn’t call this compounding friendly and it may elicit hisses tank-side or in the QC lab. I would just formulate with a pre-buffer like sodium citrate. For every 1% of this preservative blend, start with 1.5% sodium citrate and see how that helps reduce drift.

Also, totally unrelated, I’m not a fan of this preservative system in high-aqueous systems. Aside from the fact I’m triggered by the odor from a 2014 project gone wrong, I find that it precipitates out of solution over time. I would recommend it for serums and lotions. 

---

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 and is the co-host of The Beauty Brains podcast. You can find her on Instagram at @cosmetic_chemist. Do you have a formulation question you want answered? Email her at the address above.