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Separation and discoloration of a cream.
Hello everyone. I made a face cream that’s at pH 4.6-4.9 (“skin whitening”). There are two problems with it in regards to stability:
1. The first time I made it, I added magnesium ascorbyl phosphate, niacinamide and kojic acid dipalmitate (0.5%, 2.5% and 1% respectively). This didn’t change the aesthetics of the cream but after 2 weeks in a 50C oven, the product turned peach-colored. However, the pH was stable and the fragrance did not go sour. The emulsion was stable as well. There were also no issues after putting the cream through 3 freeze/thaw cycles, and UV light from a windowsill had no effect on the color.2. I remade the cream without the additives, thinking that the vitamins started oxidizing in the heat (or they’re just not that stable at such a low pH). This time, however, after a few days in an oven, the cream started separating. I remade it again with a different lot # of emulsifying wax NF; same issue took place. Also, after freeze/thaw, the cream lost some of its gloss and started getting paste-like. No discoloration at any temperature or daylight exposure, and the pH and fragrance are fine.I guess I’m not sure what I’m doing wrong. The cream itself is quite nice in my opinion: very light and “fresh” feeling, non-greasy, blends into the skin quickly. I’m not attached to the vitamins, and my priority would be to keep the pH between 4.5 and 4.9.In no particular order, these are my ingredients minus the three vitamins mentioned above:Water, xanthan gum, glycerin, allantoin, water-soluble plant extract, phenoxyethanol/ethylhexylglycerin, emulsifying wax NF, jojoba butter*, cetearyl alcohol, c16-18 alkyl benzoate, lauryl laurate, tocopheryl acetate, cyclopentasiloxane, essential oil (fragrance), glycolic acid, NaOH*proprietary blend that includes some hydrogenated oilsIf anyone could point me in the right direction that would be great. Thank you! -
7 Replies
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Just my two cents:1- MAP oxides and produces an orange by product. It’s a characteristic of VitaminC. So you’re correct to make it without the actives.
2- Try testing your emulsifier system. Increase and decreasing your emuslifier wax and see the effect. I doubt lot make a difference in the quality of your emulsion but the amount of emulsifier does. -
The ethylhexylglycerin in your phenoxyethanol / ethylhexylglycerin presevative can cause emulsion instability. Did you include it in your HLB calculations.
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What temp was the oven you refer to? 50c is approaching the melting point of some fatty acids - this will give you a yes answer but not always a no answer.
What % of D5 do you have? Silicones can be more challenging to emulsify. Sepigel 305 does a nice job here but if you’d like to keep the pH low try simulgel NS.Have you tried using the HLB system? Downloadable self-explanatory calculator here: - http://www.makingskincare.com/hlb-calculator/Lastly, try adding carbomer - gives good high temp stability. -
agree with @MakingSkincare - passes in extreme test conditions are positive proof of stability, but failures are generally less meaningfulalso agree with @Beaver about vitamin C; frankly I’d be surprised if it didn’t discolour at 50°C
the fact that your cream looks paste-like after several freeze/thaw cycles indicates the dispersed droplets are coalescing (therefore not reflecting as much light) and suggests your emulsification system is weak
personally I’d add something like Arlacel 170 (INCI: Glyceryl Stearate / PEG-100 Stearate) or Emulgade F (INCI: Cetearyl Alcohol / PEG-40 Castor Oil / Sodium Cetearyl Sulfate) as a secondary emulsifier
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@MakingSkincare actually the temperature is 45C, not 50. That was my mistake at misreading the oven settings.
I’ll try some of your suggestions. -
Well, if you leave out the MgAscorbylPhosphate, Niacinamide and Kojic Acid … then your formulation is not going to be a skin whitening cream … it will essentially be a very weak glycolic acid exfoliating cream since the glycolic will be most effective at pH 3.5.
As mentioned above … did you use the HLB system? If not, you probably should to get the proper ratios of emulsifiers/oils.Frankly, I would leave out the cyclopentasiloxane and the glycolic acid/NaOH. MgAscPhosphate will be most stable at pH 7.0 and Niacinamide at 6.0. So, if your objective is to form a skin whitening cream, best you formulate to the pH where the skin whitening actives are most stable. As it is, you’re trying to bridge the pH gap between the glycolic acid and the vitamins and getting the worst of both worlds. -
Unless the undefined “water soluble plant extract” is licorice root extract or daisy blossom extract or some other skin whitening extract.
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