![]() Nomenclature surrounding UV-filter types is important, considering their scientific, commercial and popular usage. ZnO and TiO 2 are commonly employed to impede UV-A and UV-B transmission, respectively. The FDA also approved the use of two inorganic “filters” that impede UV-A and UV-B transmission: titanium dioxide (TiO 2) and zinc oxide (ZnO). Filters that provide coverage of the UV-A region are particularly important because up to 95% of UV radiation reaching the Earth’s surface is UV-A. 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). 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. Within the past few years, there have been multiple highly publicized studies regarding the potential hazards of small-molecule based sunscreens on human health and aquatic environments. The limited list of chemicals available for use as sun protecting active ingredients is concerning, especially considering the emerging public scrutiny of ingredients. Sunscreen efficacy and safety is of paramount importance for both human health and the environment. ![]() 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. 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. Changes in UV absorbance were minimal for all five small-molecule-based mixtures without zinc oxide. We evaluated the photostability and toxicity of these mixtures in the absence and presence of zinc oxide after UV exposure for two hours. ![]() 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. 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. ![]() However, the photostability of sunscreens has been shown to be highly dependent on the mixture of chemicals present. Sunscreen safety and efficacy is generally evaluated based upon the properties of the individual chemicals in a formulation. ![]()
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