## 1 Introduction
In addition, the development of sustainable treatment techniques that ensure both efficiency and environmental friendliness is required. These technologies must reduce environmental impacts, minimize the waste generated, and be economically viable for industrial scale [12,15]. Finally, addressing regulatory gaps and creating clear standards is necessary for the wider use of grape by-product extracts in industrial applications. In the European Union, their use in food and cosme remains limited, as there are no clear guidelines on permitted limits and safety procedures [16,17]. Depending on the geographical location, climate, temperatures, and soil type, different grape varieties are grown, resulting in a variation in bioactive molecule content between different grape varieties, especially between red and white grapes [3]. However, several studies have shown that in most varieties the bioactive components of grapes remain after the vinicitation process in the by-products, i.e., in the grape seeds [1]. Thus, grape pomace, which is a mixture of seeds, stems, and skins, has been found to be rich in valuable compounds such as fatty acids, proteins, carbohydrates, and polyphenols [3]. With proper processing, these compounds present in the core of grapes can offer a wide variety of beneficial properties to the health and appearance of the skin, as they offer antioxidant, antifungal, and antimicrobial action [3]. Polyphenols, including proanthocyanidins and resveratrol, have been shown to modulate critical cellular pathways involved in skin health [18]. In keratinocytes, these compounds reduce oxidative stress and inflammation by lowering reactive oxygen species (ROS) and pro-inflammatory cytokine levels, while also protecting DNA from UV-induced damage. Similarly, in fibroblasts, polyphenols enhance the expression of genes like SIRT1 and HSP47, which are linked to anti-aging processes, promoting skin elasticity and hydration [18; 19; 20]. These properties also make grape by-products particularly useful in cosmetic products, especially in anti-aging and skin-whitening products. They can be used to improve skin hydration and softness, reducing roughness, wrinkle depth, redness, and hyperpigmentation. They also protect the skin from oxidative stress and UV damage, acting as photo protectants with a high sun protection factor. In addition, they can inhibit the activity of proteinase, collagenase, and elastase, which are important for the degradation of collagen and elastin in the skin, thus providing firmness and elasticity. Because of these, grape by-products are active ingredients in cosmetics aimed at improving the texture, appearance, and general health of the skin, making it more youthful and resistant to environmental aggressions [3]. This paper aims to provide a comprehensive overview of the use of grape by-products as active ingredients in cosmetics, based on the latest available literature. It focuses on bioactive compounds, such as phenolic compounds and unsaturated fatty acids, and their benefits for skin health and appearance. Furthermore, it highlights advanced extraction techniques that enhance their stability and bioavailability. The innovation of this review lies in associating these bioactive ingredients with molecular mechanisms of action, including the SIRT1 and HSP47 pathways, offering a sustainable and natural alternative to synthetic additives in the cosmetics industry.