Combining the Salt‐Tolerant Plants Limonium algarvense Erben and Polygonum maritimum L. Promotes Synergistic Bioactivities for Enhanced Cosmetic Applications

ABSTRACT The demand for natural and sustainable ingredients in dermo‐cosmetic formulations has promoted the use of coastal salt‐tolerant plants as novel bioresources. This study evaluated aqueous extracts of Limonium algarvense and Polygonum maritimum , two salt‐tolerant coastal plants and their mixtures (3:1, 1:1, 1:3, w/w) for antioxidant, metal‐chelating, enzyme‐inhibitory, antimicrobial and cytotoxic properties. Chemical profiling revealed diverse phenolic signatures dominated by catechin, myricetin and quercetin derivatives, which are known contributors to antioxidant and enzyme‐modulating activity. L. algarvense showed the strongest superoxide‐scavenging activity (EC 50 = 219 µg/mL), while P. maritimum was the most effective hyaluronidase inhibitor (EC 50 = 42.9 µg/mL). The 1:3 mixture displayed the most pronounced synergistic behaviour, notably in hydroxyl‐radical scavenging (EC 50 = 62.7 µg/mL; SE = 0.08) and antibacterial activity against Escherichia coli (MIC = 39.68 µg/mL; SE = 0.31). The 3:1 mixture showed enhanced elastase inhibition (EC 50 = 33.0 µg/mL; SE = 0.76) and increased copper‐chelating capacity (EC 50 = 533 µg/mL, SE = 0.52). All extracts maintained cell viability above 90%, supporting their safety for topical applications. Together, these results indicate that L. algarvense and P. maritimum deliver complementary and synergistic activities relevant to dermo‐cosmetic innovation, emphasising their potential as sustainable, multifunctional ingredients compatible with saline agriculture and low‐freshwater production systems.