The skin microbiota, with its millions of bacteria, fungi, and viruses, plays a key role in balancing the health of the skin and scalp. Its continuous exposure to potentially harmful stressors can lead to abnormalities such as local dysbiosis, altered barrier function, pathobiont overabundance, and infections often sustained by multidrug-resistant bacteria. These factors contribute to skin impairment, deregulation of immune response, and chronic inflammation, with local and systemic consequences. In this scenario, according to the needs of the bio-circular-green economy model, novel harmless strategies, both for regulating the diverse epidermal infectious and inflammatory processes and for preserving or restoring the host skin eubiosis and barrier selectivity, are requested. Vitis vinifera L. leaves and their derived extracts are rich in plant secondary metabolites, such as polyphenols, with antioxidant, anti-inflammatory, antimicrobial, and immunomodulatory properties that can be further exploited through microbe-driven fermentation processes. On this premise, this literature review aims to provide an informative summary of the most updated evidence on their interactions with skin commensals and pathogens and on their ability to manage inflammatory conditions and restore microbial biodiversity. The emerging research showcases the potential novel beneficial ingredients for addressing various skincare concerns and advancing the cosmeceutics field as well.

Vitis vinifera L. leaves represent one of the most phenolic-rich grapevine biomasses, exhibiting a broad spectrum of biological activities, including prebiotic and microbiota-modulating ones. However, as they are mainly regarded as agro-industrial waste, they are still an underexploited resource. Probiotic-driven fermentation may offer a promising strategy to enhance their bioactive potential while addressing this challenge. The aim of this study was to evaluate the effects of the in vitro fermentation of Vitis vinifera L. leaf extract (VVLE) by Lactiplantibacillus plantarum PBS067 in terms of phenolic content, antioxidant activity, lactic acid and protein content, and metabolomic profile. Our analysis shows the prebiotic activity of VVLE, as VVLE-supplemented medium allowed probiotic growth without toxic effects. Leaves fermentation led to a significant enrichment in lactic acid and the biotransformation of complex plant-secondary metabolites into smaller derivatives. However, VVLE antioxidant capacity slightly decreased after the fermentation, likely due to the phenolic conversion itself. These results highlight how controlled lacto-fermentation valorizes grapevine leaves, transforming them into sustainable upcycled bioactive products with potential applications within cosmetics, pharmaceuticals, nutraceuticals and complementary medical product sectors. Key points: • L. plantarum PBS067 thrives in medium supplemented with polyphenol-rich leaf extract • L. plantarum PBS067-driven fermentation modulates VVLE phytochemical profile • L. plantarum PBS067-driven fermentation valorizes viticulture by-products