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  • Product Compatibility Questions for Chemists…

    Posted by Anonymous on March 23, 2014 at 3:56 pm

    I am wondering how commercial, chemical sunscreens (non-mineral) will work in combination with a shielding-type lotion I’ve made for myself. I’ll use this lotion to mitigate TEWL with things like dimethicone (5%), allantoin (.5%), hydro oat (4%), aloe (12%)-and other things like niacinamide and panthenol in a cationic (BTMS 50) emulsion with another cationic, Polyquat 7. I’m excited to road-test this for myself, but know that I’ll also want UV protection.

    Now that I’ve got all these things that claim to “bond” and/or form a film on the outer layer of skin, I’m am curious about how I should apply a sunscreen to get its full benefit. How can I use both?

    So, do the ingredients I’ve described in my lotion REALLY form a barrier on skin that will prevent a suncreen from “absorbing” into skin, as described on sunscreen instructions? (In which case, I would apply sunscreen first-but re-application throughout the day would be moot.)


    My lotion WILL form a barrier, but chemical sunscreen molecules are small enough to penetrate any film that’s created. (I can apply sunscreen before and/or after, to good effect.)


    Chemical sunscreens can absorb UV rays just as well from the surface of a film on the skin. (I can apply my lotion first, then follow-up with sunscreen as needed throughout the day.)

    So, what do you all think? I’m not sure I’ve posed these questions in the most succinct way, but hope you get the gist-and have some thoughts to share. Thanks!

    mikebavington replied 10 years, 4 months ago 2 Members · 2 Replies
  • 2 Replies
  • alchemist

    March 25, 2014 at 11:02 pm

    Sunscreens don’t absorb into the skin (to any significant level) they work in a film on the surface of the skin.

  • mikebavington

    March 26, 2014 at 2:00 pm

    If you are composing a sunscreen inspired TEWL lotion that uses Dimethicone, I suggest you use some PEG Dimethicone based emulsifiers to enable your water based ingredients to mix with your silicones, and in the process, add to the SPF factor of the final product. Surfactants such as PEG-10 Dimethicone, PEG - 12 Dimethicone, PEG/PPG-18 Dimethicone etc.

    Regarding Dimethicone, it, by itself, provides a respectable SPF factor. Read this link (pdf) on silicones and SPF, from Dow:


    Many scar gels use silicones for healing and for sunscreen protection while the scar heals.

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