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Question about Iron Oxide as Sunscreen
Is there any minimum concentration of iron oxide to exhibit UV protection?
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9 Replies
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Are you sure you want to use iron oxides for this purpose?
All grades of iron oxide are strongly coloured. Any amount applied to the skin will be visible and possibly/probably unwanted.
Think carefuly about user acceptibility before you proceed much further.
Regarding the specifics of your question, I doubt that anyone has investigated the spectrum absorbing qualities of iron oxides for the end uses you intend.
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Maybe what you mean is zinc oxide?
Or titanium dioxide? -
Also, Iron Oxides, due to their color, will likely heat up in intense sunlight. I can’t imagine that this would be pleasant.
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i was just planning to add iron oxide for aesthetic purposes as coloring pigment and I was just curious of the minimum conc for protection against visible light
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Back when I was working on formulating standard liquid foundations, we tested all of them for SPF, to see if we could make any claims. Most of the regular coverage formulas had a SPF of 2, the others were zero. All tinted moisturizers tested were zero. High coverage formulas and concealers got about a 4. The SPF results correlated well with the TiO2 levels - iron oxide levels had virtually no contribution to SPF at all.
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@Bobzchemist Thanks for the info.
I found this article about colored sunscreen protection against visible light using iron oxide pigments
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Visible light isn’t the problem that sunscreens are solving. SPF is a measure of how well a product protects against UV light.
Iron oxides also aren’t on the FDA’s list of sunscreen actives.
http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=352.10 -
WHY not use a mixture of ZnO and TiO2 which are approved.Critical wavelength for UVA (370nm) is easily achieved using relatively low levels of the combination?
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Perry and Dr. Bob both have a good point. Since even mentioning anywhere that your SPF coverage had anything to do with iron oxides could result in the FDA forcing a recall of your product, why would you bother?
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