Development and Preliminary Physical Stability Assessment of Anhydrous Kojic Acid–Tetrahexyldecyl Ascorbate Systems

Kojic acid and vitamin C are widely used depigmenting actives whose therapeutic potential is limited by pronounced instability in aqueous media. This study developed and characterized anhydrous suspensions designed to co-stabilize both compounds within a minimalist squalane-beeswax matrix. Four formulations (F1-F4), varying in active composition, were evaluated immediately after preparation, at 48 hours and after four months of storage, using electrical resistivity, optical microscopy, centrifugation and vortex testing. All suspensions displayed infinite resistivity, suggesting a water-free, non-polar system, and maintained homogeneous active dispersion without agglomeration. Centrifugation revealed composition-dependent stability, with the balanced kojic acid- tetrahexyldecyl ascorbate (THDA) ratio (F3) showing the greatest resistance to phase separation, while higher THDA loading reduced mechanical robustness. No yellowing, sedimentation or textural change occurred over four months, consistent with a sustained chemical protection. These findings validate anhydrous suspension as an effective, technologically simple strategy for stabilizing photosensitive depigmenting actives in dermatocosmetic formulations.