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Potential for Sodium Benzoate forming Benzene with Iron oxides
Just a quick ‘skin insurance’ question for the chemists in regards to negative chemical reactions that may occur by laying products:
Layer one would be a well formulated pH 5.5 moisturiser containing a small amount of Sodium Benzoate (minute, as I understand it, it is only in there due to its inclusion in one of the botanicals indigent included rather than added to the formula by the manufacturers themselves.)
Layer 2 would be a tinted sunscreen containing iron oxides and a small amount of L-Ascorbic Acid. This formula is also pH5.5
Is there a potential for benzene to form when these are layered on the skin? I am hoping no as, from what I understand from reading this forum, the pH would have to be considerably more acidic to cause an issue. None the less, better safe than sorry. I just wanted to confirm this.
Kind thanks.
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7 Replies
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For clarification, the iron oxides in the products are CI 77492, CI 77491 and CI 77499.
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for that to happen you’d need iron in solution; iron oxides are insoluble except in strong acids (e.g. hydrochloric, sulphuric), so the risk is likely negligible to nil
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The answer, obvious to me, is to remove one or both of the potentially offending materials.
Benzoic acid? Use a different brand of botanical which does not use benzoic acid as a preservative. Why are you using botanicals in a functional product like this? It is not doing anything useful.
Ascorbic acid? Plenty of other materials available which can replace this in cosmetic products.As Bill says, though, the risk is negligible.
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Thank you both.
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Out of intererest, just to broaden my understanding, could you comment further on what constitutes iron in solution? I imagine this could be found in spring/non-ionised water etc. How about the use of an iron containing compound such as brown algae in a product? Would that lend iron in solution to the mix? If so would a chelator bind this from reacting with sodium benzoate contained in another product layered on top? Kind thanks for educating me.
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https://en.wikipedia.org/wiki/Dissolution_(chemistry)#Ionic_compounds
if an ionic salt is soluble in water, and one of the ions that make up said salt contains iron, the iron is in solution once the salt has dissolved
in biological systems like brown algae (and humans, for that matter), iron is stored and transported in dedicated proteins, so the concentration of free iron is usually next to nil
even if there is any free iron, it’d be such a tiny amount, and the dilution factor in cosmetic products is so large, that the risk to the end user would be so small it may as well be non-existent
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Thank you Bill!
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