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What happens to powdered zinc oxide when you mix it with dimethicone?
  • Zuz
    Who here knows some chemistry? I need your brains!
    I've been reading about physical sunscreens. A lot. And I'm starting to wonder how, aside from the nano-particle safety controversy, zinc oxide can be a stable sunscreen applied to the skin. According to Wikipedia it's degraded by most acids, reacts slowly with fatty acids in oils to form carboxylates, and when it's combined with water and UV light on the skin hydrogen peroxide is formed?! I guess that's why regular old zinc or titanium oxide sunscreens are so very greasy?

    So I read about dimethicone-coated micronized zinc, Z-Cote hp1, but there's not a product out there with it I can afford (except Blue Lizard's face, which also has some things I don't want to use year round.) And of course, I think to myself, how hard can it be to coat some zinc oxide with some dimethicone? I mean I read a little about the process and yes, it sounded hard... but hey, I don't need the best-coated zinc oxide in the world, I'm sure it doesn't have to be all that...
    Sooooo... Yep, my idea is to buy some dimethicone, micronized zinc oxide, stir a lot... really... until I get a paste I can mix with my moisturizer... either pour it in and, again, stir a lot, or if that's really not going to work, on the side like a primer, until I get bored with the whole routine...

    How do you figure that'll work out for me?

    (Don't worry, for sunburn protection I'll still use a chemical sunscreen. But I really want a safe moisturizer with some physical UVA protection, without uncoated micronized zinc, that doesn't leave me extremely greasy or white, that I can afford.)
  • Zuz
    Related question, sort of -

    what happens when you mix benzoyl peroxide with zinc oxide or titanium dioxide? On your skin? I assume the micronized zinc & titanium oxides in my mineral foundations can mix with my acne medication to some degree.
  • lelalelalelalela
    Both zinc oxide and titanium dioxide naturally occurs as a powder, so neither is naturally greasy, they are only greasy when mixed with typical ingredients used in sunscreens such as thickeners and emulsifiers. They are also naturally white in color and there's no way either can ever leave no white cast, unless you mixed it with pigment and made mineral makeup. Dimethicone itself feels greasy unless it's chemically bonded with polymers to make it mattifying.

    I used to play kitchen chemist a lot, ordering ingredients off the internet and playing around, but honestly, internet research is not a chemistry degree and my experiments would almost always fail. It's really hard to make products that are cosmetically appealing and effective, that's why not just any old joe can be a cosmetic chemist. I would suggest using a silicone based mattifying spf foundation that has titanium dioxide or zinc oxide as part of the sunscreen. I personally love L'oreal true match, it's an spf of 17, part of the sunscreen is titanium dioxide, it's super light, blendable, mattifying and it's light to medium coverage. The price is under 20 dollars too.
  • tom_guy85
    Hmmmmm, I cant say you've got anything to worry about from a chemistry point of view regarding normal zinc oxide powder. Reactions would occur too slowly to significantly hinder the performance of the zinc. Also, to form peroxides you would need more heat than the ambient temperature on the skin and a significant amount of water, which is non-existent after application.

    As for the greasy feel, most sunscreens contain silicone oils or other lubricants so will naturally feel greasy, least in my experience.

    I cannot see any problems with benzoyl peroxide, as it degrades almost instantly on contact with the skin, so there's no way any reaction with zinc would compete. Both are found in minute proportions in cosmetics anyway, that any adverse reactions would be minimal, so it seems.
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