A standard scoring method for measuring white cast of mineral sunscreens and improving user compliance across diverse skin tones

Using broad-spectrum sunscreen is an effective practice for preventing skin cancers caused by ultraviolet (UV) radiation. Mineral sunscreens containing zinc oxide (ZnO) and titanium dioxide (TiO2) as physical UV filters are suitable for individuals with sensitive skin or allergies to chemical UV filters. Consumer compliance with sunscreen application depends largely on its cosmetic elegance, especially regarding white cast. Despite this, there is no official method to quantify white cast and help design sunscreens for diverse skin tones. To address this gap, we developed validated white cast scoring protocols that combine 1) subjective consumer feedback on formulations containing ZnO concentrations ranging from 0-30% with 2) objective L* measurements (whiteness) determined after sunscreen application. Our findings demonstrate a strong correlation between increasing ZnO percentages and higher L* values, resulting in a more visible white cast. White cast scores for the ZnO formulations were substantially consistent across both in vivo and in vitro methodologies, with higher ZnO concentrations producing unacceptable levels of white cast. This study provides a white cast scoring system as a quantitative tool for evaluating and refining mineral sunscreen formulations, contributing to the development of more cosmetically elegant sunscreens suitable for a wide range of skin tones.