Natural Sunscreens Based on Nanoparticles of Modified Kraft Lignin (CatLignin)

Commercial chemical sunscreens have a high content of synthetic ultraviolet (UV) actives that have caused widespread damage to marine ecosystems and may have adverse health effects in humans. In the present work, safer bio-based sunscreens with lignin UV absorbers were developed to address this issue. Partly demethylated and otherwise altered kraft lignins, the so-called CatLignins with abundant phenolic hydroxyl auxochromes and catechol units, outperformed regular kraft lignins as sunscreen UV absorbers in terms of sun protection factor (UVB–SPF) and UVA–UVB transmittance. Converting lignins to nanoparticles significantly enhanced sunscreen performance. The best lignin sunscreen, containing nanoparticles of hardwood CatLignin, had a UV transmittance of only 0.5–3.8% over the entire UVA–UVB region compared to 2.7–51.1% of a commercial SPF 15 sunscreen. Lignin-based sunscreens are particularly suitable for dark-tinted SPF cosmetics.