Natural Deep Eutectic Solvents as Innovative Multifunctional Ingredients in Cosmetic Formulations: Scaling up from Lab to Industry

In recent years, the cosmetic and dermo-cosmetic industries have experienced a shift driven by the principles of green chemistry and the growing consumer demand for clean-beauty platforms. Conventional personal care formulations heavily rely on synthetic glycols, petroleum-derived penetration enhancers, and heavy chemical preservatives to stabilize active ingredients and optimize topical application. However, these ingredients are increasingly scrutinized due to their associated carbon footprints and processing inefficiencies. Consequently, the development of multi-functional, bio-based, and ecologically sustainable solvents has emerged as a primary frontier in modern cosmetic engineering. For the first time, this study focused on determining the physicochemical properties and direct cosmetic application potential of Natural Deep Eutectic Solvents (NADESs) based on 1,3-propanediol (PDO) and glycerin (GLY) paired with organic acids (citric, succinic, malic, and lactic) at a 6:1 molar ratio. Unlike traditional, highly viscous eutectic mixtures, the engineered NADESs successfully optimized liquid dynamic viscosities, overcoming a major barrier for topical application. The new NADESs and, for comparison, a physical mixture of their substrates were incorporated into aqueous serums and O/W emulsions. Accelerated stability trials (40 °C/4 °C, 3 months) combined with pH monitoring revealed that while liquid serums maintained exceptional stability, the emulsion formulations were highly dependent on the specific acid structures. All formulations of cosmetics demonstrated very good radical scavenging activity (up to 89% DPPH inhibition) and microbiological purity, complying with the ISO 17516:2014 standard. Furthermore, in vivo sensory evaluations visualized via heatmaps confirmed that NADESs effectively eliminated the characteristic “sticky effect” of polyols, significantly enhancing product ease of application on skin. This study provides the first systematic evidence that these NADESs offer seamless cold-process compounding, reduced homogenization times, and simplified single-pot operations. Consequently, this work establishes a novel, clean-beauty-compliant platform for advanced dermo-cosmetic manufacturing.