October 14, 2021

expert reaction study looking at mixing mineral and chemical sunscreens and efficacy and toxicology under UV irradiation

A study published in Photochemical & Photobiological Sciences suggests mixing chemical sunscreen mixtures with zinc oxide may limit protection against UVA.

Prof Oliver Jones, Professor of Analytical Chemistry and Associate Dean of Biosciences and Food Technology, RMIT University In Melbourne Australia, said:

“The paper is interesting and thought provoking. The main result – that zinc oxide may cause the degradation of small, organic (carbon containing) molecules in the presence of UV light is not that surprising since both zinc oxide and titanium oxide are well known to have this property. The work does, however, highlight the importance of knowing your chemistry when you mix materials, that have previously been used separately, into a new product.

“There are, some limitations to keep in mind though.

“Firstly the authors used their own formulations for this work and did not test any commercial sunscreens, which tend to have more complex formulations. It is quite possible that if the experiment was repeated with off the shelf sunscreens the results would not be the same.

“There was also no analysis of the hybrid sunscreens after UV exposure to determine what the reaction products might have been, and the potential toxicity was assessed using a zebrafish embryo assay. While this is a well-used model for ecological toxicity testing, zebrafish embryos are not mini humans, and the results are not directly comparable.

“The central message in this paper is that sunscreens that have both small molecule and zinc oxide components may not work as well as expected and thus might be best avoided. Exploring this further may certainly prove useful. However, we still need to be sun smart. I think the risk of UV damage from not using any sunscreen at all is higher than even the worst-case scenario in this study.

“So in short, don’t panic and keep using sunscreen”.

Prof Winston Morgan, Reader In Toxicology And Clinical Biochemistry, University of East London, said:

“The press release accurately reflects this study. There are numerous limitations in this study, some of which are highlighted by the authors, but also some around the concentrations used and how they relate to real world situations. This limits what conclusions can be drawn from the study. It would have been better if the study had looked at human skin cells, rather than zebrafish embryos. The degradation of the protection is of interest but it’s hard to assess the toxicity from this study alone. The study did not tell us anything about uptake of molecules so it is too much of a leap to draw any conclusions about sunscreen use in humans from these findings. Much further research is required and we next need to do in-vivo animal studies.  My concern is that the public may see headlines from this study warning about sunscreen mixing and think that all sunscreens are not safe which would be wrong and counterproductive.”

‘Zinc oxide‑induced changes to sunscreen ingredient efficacy and toxicity under UV irradiation’ by Aurora L. Ginzburg was published in Photochemical & Photobiological Sciences at 01:00 UK time on Thursday 14th October 2021.

DOI: 10.1007/s43630-021-00101-2

Declared interests

Prof Jones: “I have no conflicts of interest to declare.”

Prof Morgan: “no interests”