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SPF with 6% zinc oxide test
We sent a batch of moisturizer day cream with lots of Jojoba oil, Raspberry oil and 6% of minceonized (not nano) zinc oxide for proffesional testing. The result was 1-3 SPF!! But as far as I know - 1% zinc oxide gives aprox. 1,5 SPF. What could be wrong here? I was sure SPF should be around 6-7 SPF
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14 Replies
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tinas said:We sent a batch of moisturizer day cream with lots of Jojoba oil, Raspberry oil and 6% of minceonized (not nano) zinc oxide for proffesional testing. The result was 1-3 SPF!! But as far as I know - 1% zinc oxide gives aprox. 1,5 SPF. What could be wrong here? I was sure SPF should be around 6-7 SPGood day. What instrument did your use to measure the SPF of your cream?
Thank you
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It was a proff. company in Germany, so I can not doght the rapport!
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https://www.sunscreensimulator.basf.com/Sunscreen_Simulator/login
You may use this to measure the SPF of the sunscreen in your formulation. It was shared to me by a fellow cosmetics formulator.
Thank you.
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Thank you, but the company we used is professional, so I do not doubt the result of the test. But do you have any idea why 6% micronized zinc and also a lot of raspberry oil and jojoba oil is not more than maximum SPF3? Does the zinc “soak” into the skin since this is a moisturizer (O/W) and not sunscreen cream?
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It could well be that the Zinc Oxide was not evenly dispersed in your sample. The SPF measurement is how much longer it takes the skin to burn with the sunblock applied versus no sunblock. If ZnO is not evenly dispersed in your sample, parts of the skin will essentially have no coverage and the testers will detect irritation early in the testing cycle, hence the low SPF rating even though you have ZnO in the formula.
Did you use a premixed blend or are you charging ZnO powder to your formulation … if you are adding a powder, are you adding a dispersant such as polyhydroxystearic acid?
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We dissolve sodium citrate first in hot water and then zinc oxide for lotion/cream.what is role of polyhydroxystearic acid? -
It’s a dispersing agent that reduces the viscosity of the ZnO (or TiO2) powder blend in solvent allowing you to get a higher load of powder in the solvent with more even dispersion of the powder.
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Mark: Yes, I think you have a point there! I warmed “lots of” meadowfoam oil, and blend the ZnO powder and used it after maybe 6 hours. Is there any ecoapproved dispersant I can use? (This is a moisturizer - O/W, and not a typical sunscreen cream)
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Kesterwax K-60P from Koster Keunen is NPA certified polyhydroxystearic acid.
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@tinas, do you have a formulation you could share with us? Without that, we’re gonna continue to help only to find our suggestions are unhelpful/inapplicable.
It it might seem backwards but as far as I know (which isn’t much), a regular lotion + SPF is actually more difficult than what we think of as standard sunscreen.
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You are right Sponge - I will try different dispersants to make an even “fluid” of zinc and titanium dioxide, and if I am satisfied, I share with you all. I think lots of the premade fluide SPF like Solaveil etc. feels so “fat” and thick to use in a moisturizer, and I have to use a lot of this stuff - maybe 20% in a cream. Hopefully I can develope a fluid SPF that is better for the skin.
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#tinas you can find great zinc dispersions from Antaria Australia- called Zinclear Zinc Dispersions in Jojoba, MCT & Coco-caprylate. They get samples out to you very quickly.
Hope this helps -
Thank you so much Dr Catherine - have you or someone tried Ethochel Standard 100 Premium (3% in MCT)?
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No I have not used that one, but I agree with Mark, the Zn may not have been evenly dispersed. That’s why the Zinclear dispersions are so good, you don’t have to worry about it at all. Worth a try!
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