Structural color generation in lipid-based cosmetics: Lamellar nanosheets from skin-identical fatty acids

There is growing interest in pigment-free, biocompatible systems that generate structural color for cosmetic applications. This study presents pearlescent cosmetic formulations composed of skin-identical long-chain fatty acids, stearic acid (C18) and behenic acid (C22), that self-organize into multilamellar nanosheet structures in aqueous media. These formulations exhibited vivid, composition-dependent structural colors in the visible region, consistent with constructive interference of reflected light within nanosheet-based lamellar domains. Wavelength shifts were observed in the reflectance spectra as the ratio of stearic to behenic acid varied, indicating tunable optical properties. SAXS confirmed multilamellar structures with interlamellar spacing that varied systematically with composition. This study is the first to demonstrate structural color generation from physiologically relevant fatty acids naturally present in the human stratum corneum. These findings offer a skin-compatible, pigment-free design strategy for multifunctional cosmetic formulations that combine visual aesthetics with biological relevance.