Evaluating the suitability of six hydrophobic natural eutectic solvents as the internal phase in a cosmetic cream...

This work evaluates whether hydrophobic natural eutectic solvents can replace the conventional oil phase in cosmetic creams while maintaining or improving physicochemical stability, rheological structure, and sensory performance. The goal is to develop formulations that combine sustainability, regulatory compliance, and sensory performance while remaining compatible with standard low-energy manufacturing processes.

Six HNESs systems composed of regulation-compliant fatty acids, menthol, and alkane diols were characterized for viscosity, density, and refractive index. Model oil-in-water creams were prepared using cold homogenization to ensure scalability and energy efficiency. Emulsion stability was assessed over 30 days in accelerated ageing conditions using multiple light scattering and pH tracking; rheology was evaluated via flow curves and strain sweep tests; applicative sensory properties (spreading resistance, gloss, stickiness, residual film wettability) were instrumentally measured on a non-biological skin surrogate.

Solvent composition governed emulsion behaviour. Fatty acid-based systems produced small, stable droplets, low bulk viscosity, and favourable sensory attributes (high lubrication, reduced stickiness), while maintaining dermatologically acceptable pH. Menthol-containing systems exhibited higher viscosities and strong gel-like networks but showed physical instability under storage. Alkane diol-rich systems improved lubrication and gloss yet displayed larger droplet growth and pH drift, indicating weaker long-term stability. Across all creams, residual films decreased the water contact angle markedly, evidencing hydrophilic surface behaviour after application, and immediate gloss increased versus triglycerides control.

HNESs can function as structural oily phase substitutes in creams prepared by low-energy processes, enabling sustainable, regulation-compliant formulations with desirable sensory profiles. Fatty acid-based systems offer the most robust balance of stability and user experience, whereas menthol- and alkane diol-rich systems require compositional optimization to mitigate storage instability while preserving sensory benefits.