Optical and structural properties of sunscreens evaluated by physical techniques with emphasis on zinc oxide: A...

Zinc oxide (ZnO) has emerged as a prominent inorganic UV filter due to its broad-spectrum efficacy, photochemical stability, and biocompatibility. This study presents a critical overview of the physicochemical properties and performance of ZnO based sunscrrens and emphasizes the role of physical techniques, such as UV-Vis spectrophotometry, TGA, SEM/TEM, XRD, and fluorescence imaging, in the structural, morphological, and functional evaluation of formulations. Despite advancements, challenges persist, notably the lack of standardized in vitro and in vivo SPF protocols, discrepancies in UVA protection assessment, and limited data on the long-term toxicity and environmental impact of ZnO nanoparticles. Innovative strategies, including encapsulation in biopolymers and surface modification with inert coatings, have shown promise in improving cosmetic acceptability and reducing ROS generation. The integration of these technological approaches with robust physicochemical analysis is key to developing safer, more effective, and environmentally responsible photoprotective systems. ZnO remains a highly promising UV filter, and its optimal use depends on scientifically validated methodologies and interdisciplinary innovation.