Six Eutectic Solvents, One Question: Can the Oil Phase of a Cream Be Replaced Entirely?

A cream's oil phase rarely gets much credit. It sits under the emulsifier, the thickener and the humectant, doing the quiet work of carrying emollience and structure. A new study in the International Journal of Cosmetic Science asks what happens when that oil phase is replaced entirely, not with another plant oil or silicone, but with a eutectic mixture that behaves like a liquid only because two solid ingredients happen to melt each other.

The research, led by A. Verger and colleagues including R. Grard, E. Vrignaud, M. Grisel and E. Munnier, tested six hydrophobic natural eutectic solvents (HNESs) as drop-in substitutes for the triglyceride oils that normally form the internal phase of an oil-in-water cream. Each HNES was built from pairings of regulation-compliant fatty acids, menthol and alkane diols, blended until the mixture's melting point dropped low enough to stay liquid at room temperature. That eutectic trick is also what let the team keep the manufacturing process gentle: creams were made by cold homogenization, skipping the heating and cooling cycles that conventional oil-in-water emulsions usually need.

The formulation question the paper is really asking is whether a sustainable solvent swap can hold up its end of the whole system, not just its own chemistry. An oil phase has to cooperate with the emulsifier that stabilizes droplets at the oil-water interface, resist the pH drift that erodes preservative efficacy, and still deliver the glide and finish a user expects on skin. Swap one ingredient and every downstream property can shift: droplet size, viscosity, gel network, residual film.

Over 30 days of accelerated aging, the three HNES chemistries split into distinct behaviors. Fatty-acid-based systems produced small, stable droplets and low bulk viscosity while holding a dermatologically acceptable pH, which the authors identify as the strongest overall balance of stability and sensory performance. Menthol-containing systems built strong gel-like networks, measured through flow curves and strain sweep tests, but that same internal structure made them physically unstable in storage. Alkane-diol-rich systems improved lubrication and gloss on application, yet their droplets grew larger over time and their pH drifted, a sign of weaker long-term stability that the paper flags as needing compositional work before use in a real product.

The sensory side of the testing used a non-biological skin surrogate to measure spreading resistance, gloss, stickiness and the wettability of the residual film left behind. Across all six systems, that residual film sharply lowered the water contact angle on the surrogate surface, meaning the dried-down finish read as more hydrophilic than the triglyceride control, and immediate gloss came in higher as well. For a formulator, that is the detail that matters: a biosourced oil-phase substitute that does not just stabilize in the jar but changes how the product feels and looks the moment it is rubbed in, down to the angle a droplet of water makes on the skin afterward.