Zinc oxide-induced changes to sunscreen ingredient efficacy and toxicity under UV irradiation

Aurora L Ginzburg,Richard S Blackburn,Robyn L Tanguay,Lisa Truong,James E Hutchison,Claudia Santillan

doi:10.1007/s43630-021-00101-2

Aurora L Ginzburg, Richard S Blackburn + Show 4 more

Open Access

https://doi.org/10.1007/s43630-021-00101-2

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Abstract

Sunscreen safety and efficacy is generally evaluated based upon the properties of the individual chemicals in a formulation. However, the photostability of sunscreens has been shown to be highly dependent on the mixture of chemicals present. To better understand how sunscreen formulation influences stability, and to establish a foundation for probing the influence of zinc oxide additives, we formulated five different small-molecule based ultraviolet-filter (UV-filter) mixtures with a Sun Protection Factor (SPF) of 15. These mixtures contained active ingredients approved in either the United States or European Union and were designed to represent formulations of actual products on the market. We evaluated the photostability and toxicity of these mixtures in the absence and presence of zinc oxide after UV exposure for two hours. Changes in UV absorbance were minimal for all five small-molecule-based mixtures without zinc oxide. The presence of either micro- or nano-sized zinc oxide caused significant small-molecule photodegradation and the degraded mixtures exhibited higher levels of toxicity in embryonic zebrafish assays. This study suggests that caution must be taken when formulating sunscreens containing both zinc oxide and small-molecule UV-filters to avoid unintended consequences during use.Graphic abstract

Highlights

Sunscreen efficacy and safety is of paramount importance for both human health [1] and the environment [2]
These mixtures were designed based on a significant market review of commercially available products in the United States (US) and European Union (EU); using the ingredient information on the bottles, we identified trends in the most common formulation types, and formulated our own mixtures based on typical ingredient compositions
The aim of this study was to establish if certain sunscreen ingredients or formulations undergo photodegradation that can be harmful to humans and/or the environment

Summary

Introduction

Sunscreen efficacy and safety is of paramount importance for both human health [1] and the environment [2]. As of June 2021, the US Food and Drug Administration (FDA) sunscreen monograph listed only 16 ultraviolet-filters (UV-filters) (the active ingredients in sunscreens) approved for inclusion in cosmetic products. These include eight organic compounds that absorb primarily in the UV-B region (280–315 nm); four organic compounds that absorb in the UV-B and short-wave UV-A (315–340 nm) regions; but only two organic compounds that absorb primarily in the full (both short-wave and long-wave) UV-A region (315–400 nm) [3]. ZnO and T iO2 are commonly employed to impede UV-A and UV-B transmission, respectively [12, 13]

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