Skin aging is influenced by intrinsic and extrinsic factors, leading to structural changes in the skin. Current anti-aging cosmetic trends emphasize innovative natural ingredients, including plant extracts, thermal waters, and botanical hydrolats. This work aims to develop six natural anti-aging cosmetics (two serums, two day creams, and two night creams) with innovative and non-irritating profiles. The rational design was guided by market analysis and ingredient properties. Prototype formulations were created with two core mixtures: (1) natural mineral water from Termas de Unhais da Serra and Thymus × citriodorus hydrolat and (2) natural mineral water from Termas de Chaves and aqueous Vaccinium myrtillus (blueberry) extract. The products were evaluated for stability (4 °C and 40 °C, 4 weeks), safety (according to EC Regulation No. 1223/2009), including in vitro testing for skin irritation potential (epiderm model; OECD TG 439). The market study highlighted a gap in anti-aging products combining natural extracts and thermal waters. All prototypes showed desirable textures and remained stable under test conditions. No irritating effects were observed. The results support the development of effective anti-aging cosmetics rooted in natural resources. These innovative products can meet the market demand for natural and sustainable skincare solutions.

Natural mineral waters (NMWs) and plant extracts have long been valued for their therapeutic properties and skin benefits. This study investigated, in vitro, the role of five Portuguese NMWs (A-E), combined with plant extracts from five species (Ficus carica L., Rubus idaeus L., Vaccinium myrtillus, Cistus ladanifer and Thymus x citriodorus) as bioactive ingredients. Antioxidant capacity was assessed using the 2,2-Diphenyl-1-picrylhydrazyl (DPPH) method. Cellular biocompatibility was evaluated in fibroblasts (L929) and macrophages (RAW 264.7). Skin-repairing and anti-senescence properties were evaluated in L929 cells through the scratch-wound method and β-galactosidase assay. Superoxide dismutase (SOD) was quantified using a commercial kit, and lipopolysaccharide-induced reactive oxygen species (ROS) were quantified using a fluorescent probe (H₂DCFDA) in RAW 264.7. The results highlighted the beneficial impact of extracts combined with NMWs. An increase in antioxidant capacity of up to 90% was observed in mixtures comprising Ficus carica L., compared with NMWs alone. In contrast, mixtures with Cistus ladanifer showed promising anti-aging potential, with a 40% decrease in senescent cells and a 33% ROS reduction. Rubus idaeus L. extract produced an increase in cell migration capacity (up to 50%), depending on the NMW. This study highlights the potential synergism of natural ingredients with plant extracts for anti-aging.