Six hydrophobic natural eutectic solvents entered a structured comparison as the internal phase of a cosmetic cream, according to a study hosted on Wiley Online Library.

The paper, "Evaluating the suitability of six hydrophobic natural eutectic solvents as the internal phase in a cosmetic cream formulation," treats NADES — deep eutectic solvents built from renewable plant constituents — as candidates to replace or complement conventional oil phases in water-in-oil and oil-in-water systems.

For formulators, the internal phase sets viscosity, sensory profile, active solubilisation and the share of natural-origin content a brand can declare.

Why a six-solvent screen matters

Hydrophobic NADES typically pair a terpenoid — menthol or thymol — with a medium-chain fatty acid or a natural fatty alcohol. The mixture remains liquid below the melting point of either component and exhibits low volatility.

Those properties have drawn sustained interest from laboratories seeking alternatives to silicones, mineral oil and synthetic esters. Published work over the past five years has documented NADES in transdermal delivery and in extracting lipophilic actives, while data on finished emulsion stability has remained thinner.

A six-solvent evaluation under one protocol produces comparable values for texture, droplet behaviour and phase separation — the parameters a formulator actually weighs before swapping an oil phase.

What does the study change for formulators, compliance teams and buyers

Consolidating six candidates into one comparison is a procurement and compliance signal. Brands pursuing a natural-origin or "solvant vert" claim need named, traceable inputs, and eutectic blends of this type can be sourced from well-characterised components.

For regulatory teams operating under ISO 16128 natural-origin calculations, the open question is the INCI designation of a eutectic mixture. The blend can be listed as a single entry, but each constituent must remain traceable for the safety assessment under EU Cosmetics Regulation 1223/2009.

A finished dossier will need individual toxicology profiles for menthol, thymol, the fatty acid partner and any residual water content. A safety assessor also expects irritation and sensitisation data on the eutectic as a whole, since the mixture can behave differently from either component alone.

For sensory design, the trade-off sits in skin feel. Menthol- or thymol-based blends read as "active" on the skin in ways a marketing team must control. Stability testing at 4 °C, 25 °C and 40 °C for at least 12 weeks remains the minimum bar before any internal-phase switch moves to production.

Spa and clinical brands pursuing cold-process or waterless lines will see the appeal. A hydrophobic NADES phase can carry lipophilic actives such as bakuchiol, squalane alternatives and certain essential oil fractions without the greasiness of a heavy ester. The cooling effect of menthol, however, can interfere with claims of "gentle" or "sensitive-skin" positioning unless the brand rebalances with a non-menthol pair such as thymol-lauric acid.

For procurement, the shortlist gives a buyer a concrete set of samples to request. Suppliers of terpenoid and fatty-acid raw materials should expect technical enquiries from brands that have read the paper or its citation trail. Sample requests will concentrate on:

• menthol–thymol pairs
• thymol–lauric acid combinations
• fatty acid–terpene systems already referenced in extraction literature

Minimum data to request with each sample includes the molar ratio, the residual water content, the peroxide value and a certificate of analysis naming every component above 0.1 percent.

What to watch next

The next data points are the full methods section — particularly the emulsifier system, the water-to-oil ratio, the rheology curves and any preservative challenge results — and any follow-on paper that extends the screen to oxidative stability and long-term challenge testing. Brand owners who want to act before the next study can monitor the corresponding author's institutional repository or request the underlying thesis through interlibrary loan.

A Wiley-indexed comparison of six hydrophobic NADES in one cream protocol is a small brick in a wall that did not exist in trade literature three years ago.