Boosting Sunscreen Efficiency with DES‑Extracted Lignins from Olive Tree Pruning Residues

Extended exposure to ultraviolet (UV) radiation presents significant health risks, requiring the search for more effective, safe and sustainable protective measures. Lignin has emerged as a promising natural, safe, and cost-effective sunscreen alternative, due to its inherent UV shielding properties. In this study, the potential of distinct lignin samples as sunscreen components was assessed. Deep eutectic solvents were applied to previously treated olive tree pruning (autohydrolysis (L1) vs acid pretreatment (L2)) achieving high purity and antioxidant properties. The isolated lignins were incorporated into a commercial body milk with no sunscreen activity and commercial sun lotions with sun protection factors (SPF) of 15, 30, and 50. The resulting lignin- loaded creams demonstrated exceptional broad-spectrum UV absorption. Notably, the incorporation of 5% L2 into the SPF-50 sunscreen lotion yielded the most effective UV protection, achieving an SPF of approximately 170. Stability tests indicated that the sunscreens formulated with both lignins maintained excellent photostability, attributed to the synergistic interactions between lignin and the active components of commercial sunscreens against UV radiation. Additionally, the biological activity of the isolated lignins was evaluated in a mouse skin fibroblast cell line at varying concentrations (0.01-1 mL) and exposure times (24, 48, and 72 h), providing preliminary in vitro evidence of low cytotoxic response that ensure furthers validation. Overall, this study highlights the potential of the developed lignin-based sunscreens and underscores the valuable utilization of lignin derived from olive byproducts.