The dynamic duo: titanium dioxide and zinc oxide in uv-protective cosmetic formulations

Background: Photoprotection has become an essential aspect of preventing keratinocyte cancer and photoaging. However, the use of organic ultraviolet (UV) filters like oxybenzone and octinoxate has raised concerns due to their potential environmental impact and human health risks. Consequently, inorganic UV filters, namely zinc oxide (ZnO) and titanium dioxide (TiO2), have gained significant importance in discussions regarding photoprotection. These filters are employed in sunscreens as nanoparticles, with a particle size below 100 nm. The smaller size of these mineral particles enhances their cosmetic appeal as they become less visible upon application. ZnO exhibits a broad UVA-UVB absorption curve, while TiO2 provides superior UVB protection. In terms of human health risks, inorganic filters pose an extremely low risk due to their minimal percutaneous absorption. However, there is potential risk associated with inhalation, which raises concerns regarding the use of spray sunscreen products containing nanoparticles. Currently, the known environmental risk is low, although risk assessment may change as the usage of these filters increases, potentially leading to higher environmental concentrations. Nonetheless, maintaining photoprotection practices remains crucial. The public should be advised to seek shade, utilize photoprotective clothing (including hats and sunglasses), and apply sunscreens containing ZnO and TiO2 to sun-exposed skin as safe alternatives, particularly for those concerned about the emerging evidence of the environmental impact of organic UV filters. The presence of titanium dioxide and zinc oxide nanoparticles (NPs) in various commercial products, including sunscreen sprays, is widespread. Surprisingly, many of these products do not provide clear labeling regarding the presence of NPs. Consequently, this study aimed to develop a reliable method for characterizing TiO2 and ZnO NPs in sunscreen sprays. The characterization process encompassed assessing the size, shape, and composition of the particles, as well as determining their aggregation/ agglomeration characteristics. By comprehensively analyzing these parameters, a more effective understanding of the properties and behavior of TiO2 and ZnO NPs in sunscreen sprays can be obtained. This knowledge is crucial for ensuring accurate information and appropriate regulation regarding the use of NPs in cosmetic products, ultimately promoting consumer safety and informed decision-making. Results: This review provides a comprehensive analysis of titanium dioxide and zinc oxide, the two primary physical sunscreen agents, focusing on their mechanisms of action, photoprotective properties, and safety profiles in sunscreens.