Home Cosmetic Science Talk Formulating 20% Zinc Oxide for SPF 50?

  • 20% Zinc Oxide for SPF 50?

    Posted by Onur on April 12, 2024 at 10:05 am

    Check this formula by Mustela: it’s an anhydrous stick balm composed solely of natural oils, waxes, and extracts and—nothing more!

    Interestingly, there are no dispersing agents or SPF-boosting ingredients included. As per Mustela’s website, the only sunscreen agent present is non-nano Zinc Oxide, I assume the uncoated form.

    Given this formula, can we assume that 20% zinc oxide in any oil base ensures SPF 50, or at least SPF 30+? While a proper lab test is necessary to determine the SPF accurately, I’m curious if it’s feasible to achieve sufficient UVA/UVB protection that effortlessly.

    This caught my attention as I was considering creating an anhydrous SPF balm suitable for acne and fungal acne. I plan to substitute the lipids in this formula with Capric/Caprylic triglycerides, squalane, and rice bran wax (possibly Microcrystalline wax, as it’s safer for fungal acne). What are your thoughts?

    • This discussion was modified 1 month, 1 week ago by  Onur.
    suswang8 replied 3 weeks, 1 day ago 6 Members · 9 Replies
  • 9 Replies
  • LabGuy

    Member
    April 12, 2024 at 3:19 pm

    Wow, that’s impressive.

    My guess is that maybe they’re using Zinc Oxides of different sizes (it helps to balance SPF/PFA and achieve broad spectrum protection). Also, maybe there’s soothing ingredients in the formula that prevents erythema. During testing, this can help to boost the SPF value.

  • chemicalmatt

    Member
    April 16, 2024 at 11:53 am

    @Onur the SPF 50 is chiefly - but not entirely - built by nano zinc oxide, and as you surmised: likely uncoated. The other elements in an anhydrous formula such as this one also boost SPF as these are occlusives, though not UV absorbers. They function in synergy with ZnO, which deflects sunrays while the lipids block them.

    • Onur

      Member
      April 17, 2024 at 1:19 pm

      It says “NON-nano, ultra-sheer” on their website: https://www.mustelausa.com/products/spf-50-mineral-sunscreen-stick


      What does “chiefly - but not entirely” mean? Doesn’t it have to be at least SPF 50 to get this label?

      I just realized that the product contains <b style=”background-color: var(-bb-content-background-color); font-family: inherit; font-size: inherit; color: var(-bb-body-text-color);”>Octyldodecyl Olivate, it sounds like an ester. Just googled it and it says it also acts as a disperser besides being an emollient, probably an alternative to more-available Butyloctyl Salicylate.


      My question was if it would be that easy to get enough protection with such basic ingredients and if I could approach in a similar fashion. If so, I can reformulate this with non-oxidising oils such as CCT, Squalane, a synthetic wax (and Butyloctyl Salicylate + anti-redness & soothing agents like bisabolol etc). What would be some good tips?

      I’d even settle for SPF 30! Should I use more Zinc Oxide (like 25%) and mix the nano and non-nano versions at 1:1 ratio to make sure it adds more protection. What do you think?

      Lab-SPF tests are very expensive in my country, that’s why I’m trying to make sure everything is right.



      • RobboAU

        Member
        April 17, 2024 at 7:48 pm

        They’re saying non-nano their website but doesn’t mean much without knowing which definition of nano they’re using. Nano definitions used to be pretty vague and varied, I know of a USP-grade ZnO powder that was non-nano according to a specific French decree but nano according to EC 1223. That’s two contrary claims inside the EU!

        Generally speaking, ZnO’s provides SPF by scattering UV rays and to a lesser extent, absorbing and emitting it as thermal radiation. The smaller and more numerous the particles, the greater your scattering power for the same total weight. Achieving 2 SPF units per % of ZnO is quite challenging and I’d be highly skeptical of a truly “non-nano” powder achieving this.

        In regards to it being easy to get that level of protection with ZnO… yes and no. If you are working with a dry powder then you need to wet, disperse and suspend the particles. When the particles are not evenly dispersed you won’t get scattering and your SPF will be zilch. Achieving this can be very challenging, even for industry veterans.

        Using a pre-dispersed grade of ZnO in a common oil like CCT will solve the wetting and dispersing problem, so you can simply pour it into your oil phase. Now all you need to do is ensure the mixture is homogenous and has enough viscosity to prevent ZnO agglomeration.

        Get all of the above right and you’ve got a 50/50 of the in-vivo SPF being… in the ballpark.

        • Onur

          Member
          April 19, 2024 at 2:49 pm

          I think I’ll go with 15% nano (transparent) ZnO combined with 10% non-nano version. This caught my attention: https://enteknomaterials.com/en/micno-powder

          And it’s available in where I live. What do you think?

          • RobboAU

            Member
            April 20, 2024 at 10:14 pm

            I’d recommend going with their dispersions for ease of manufacturing and formulating. MicNo® DCC-N or MicNo® DAB. You can combine dry powder with the dispersions if you want, but it will make for a more challenging scale-up beyond lab bench batches. Remember, the dry powder will do nothing if it isn’t wet, dispersed and suspended properly.

  • Cafe33

    Member
    April 18, 2024 at 12:50 pm

    You may find the Manda Organic Sun Paste interesting.

    Manda Organic Sun Paste (SPF 50) ingredients (Explained) (incidecoder.com)

    Active Ingredients: Non-Nano Zinc Oxide (20%)

    Inactive Ingredients: Organic Coconut Oil, Organic Beeswax, Organic Cocoa Butter, Thanaka, Organic Cacao Powder, Organic Shea Butter, Organic Cinnamon Oil

    20% Zinc Oxide in Coconut oil, Beeswax and Cocoa Butter with an SPF 50 Rating. Not even a single ester in the formula.

    • Onur

      Member
      April 19, 2024 at 2:46 pm

      Again, how?

      Personally I can’t be 100% with those claims. INCI names are not accurate with this product, either. Cacao powder in a sunscreen formula? Why?!

  • suswang8

    Member
    April 27, 2024 at 12:25 am

    I’m sure an SPF of 30 should be taken for granted, but obviously you’d have to have the product professionally tested.

    (anhydrous 20% zinc product with SPF 40)

    https://stream2sea.com/products/spf-40-sunscreen-balm/

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