Balm with ZnO turning blue/gray

Hello! I post this product we're testing to put it under discussion. We're developing a balm with some sun protection using ZnO.
The first samples changed color from yellow/white to gray overnight, another sample containing bisabolol turned blue, is it possible that ZnO particles (not nano) accelerate oxidation?
Here is the complete list of ingredients: 
Zinc Oxide (and) Simmondsia Chinensis Seed Oil (and) Glyceryl Isostearate (and) Polyhydroxystearic Acid, Cocos Nucifera (Coconut) Oil, Sorbitan Olivate, Persea Gratissima (Avocado) Oil, Squalane, Euphorbia Cerifera (candelilla) wax, Terminalia ferdinandiana Seed Oil, Tocopherol (mixed), Daucus Carota Sativa Seed Extract CO2, Rosmarinus Officinalis (Rosemary) Leaf Oil, Coconut extract.
Which are your thoughts? Thanks!

Comments

  • Maybe contaminants from your ZnO? Try making the base without that and seeing if you have any color change on the same timescale. Does the COA for the Zinc mention any heavy metals/ purity assays?
  • PharmaPharma Member, Pharmacist
    Zinc oxide, depending on quality, can serve as catalyst for different types of chemical reactions such as oxidation also of oils.
    However, blue is often an optical illusions. Not saying that said illusion is 'harmless', it can indeed be caused by degradation but it could also be happenstance.
    I don't think it's contamination (microbes) after such a short time.
  • AleHAleH Member
    Thanks EVchem and Pharma for your comments! The COA doesn't mention anything about heavy metals or other impurities, but there's surely some interaction. We tried removing the most oxidizable ingredients and then adding them one by one. Finally, we got a stable balm without carrot oil CO2 extract and a coconut extract whose composition was not so clear. I agree with the idea that ZnO could be catalyzing some reaction, we will see how the stability studies go!

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