UV Imaging-Based Method for Quantifying Sunscreen Application and Persistence

Sunscreen effectiveness depends on formulation performance and adequate, uniform, and persistent application under real-world conditions. However, quantitatively assessing sunscreen application and persistence remains challenging. We developed a luminance-based method using ultraviolet (UV) facial imaging to derive relative image-based metrics of sunscreen application and evaluated its utility for assessing activity-related changes in sunscreen persistence. Facial UV images were acquired using the VISIA-CR® system, and mean luminance values from UV spot images were analysed at the forehead, cheeks, nose, and chin. The UV image-derived application rate was calibrated against known application doses of cream and lotion formulations. The application dose was strongly associated with the UV image-derived application rate for both formulations, with significant Spearman correlations. The mean mass applied during unguided self-application was 0.62 g, corresponding to 77.5% of the recommended facial dose (0.8 g), although UV imaging revealed heterogeneous distribution across facial regions. In the proof-of-concept evaluation, residual rates after 30 min of running were 82.8% and 73.8% for the cream and lotion formulations, respectively; after swimming, the corresponding rates were 51.9% and 50.2%. UV imaging combined with luminance analysis may provide a practical, non-invasive approach for relatively assessing sunscreen application and detecting activity-related changes in sunscreen persistence.