A recent report grabbed headlines … but a real-world, scientific worry? Not as we read it. As published in
Photochemical & Photobiological Sciences, Oregon State University researchers reported that zinc oxide sunscreens stopped working and became toxic after 2 hours of UV exposure.
Essentially, they found certain sunscreen ingredients broke down when mixed with zinc oxide and exposed to UV light.
That Conclusion unfortunately is reliant on study conditions that vastly differ from modern sunscreen manufacture and use in the real world.
What’s more, investigators looked only at uncoated zinc oxide – not the coated types of zinc oxide that we use. One of the reasons that coated zinc oxide (and titanium dioxide) was developed decades ago was to create a physical barrier around the metal particle, so it didn’t react with other substances when exposed to UV. So – aside from the fact that the study and the report are short-sighted and partial at best -- we’re not bothered a bit by that irrelevant finding.
What is troubling, though, is that the authors imply that testing mixtures of sunscreen filters for photostability isn’t commonly done and call for “the potential for zinc oxide-induced photodegradation of the whole formulation” to be considered “in the design of future cosmetic formulations”.
What is known industry-wide is that photostability formula testing has been done for decades – so it’s curious they didn’t know that.
For as long as have produced sunscreens, the photostability of every formula has been tested and reviewed by independent labs. It’s also measured by both the FDA and ISO “broad spectrum” tests – providing even more reassurance that what we offer up is genuine.
So, our belief in zinc oxide is unchanged. With one word of caution: We’ve never been fans of layering sunscreens, believing that reapplying the same sunscreen, or one with similar filters, offers the best protection and minimizes any ingredient interaction.