A Facile Workflow for Sebum Fatty Acids and Squalene Identification via Advanced Lipidomic Methodologies

Sebum fatty acids and squalene are major components of skin secretions and play a critical role in the pathogenesis of dermatological conditions through their compositional alterations. Human sebum fatty acids are uniquely diverse in their chain length, double bond positions, and chain branching; squalene is a rare component of skin secretions with six double bonds. We introduce a facile workflow for the analysis of sebum fatty acids and squalene for elucidating their contribution to the state of skin health or disease using advanced mass spectrometric methods for qualitative and quantitative analyses. Sebum from dermatologically healthy individuals was extracted, and covalent adduct chemical ionization (CACI), electron ionization (EI), and Paternò–Büchi (PB) tandem mass spectrometry (MS/MS) techniques were employed for the identification of fatty acids with varying methyl branch and/or carbon–carbon double bond positions. A method for the full structural characterization of squalene via CACI tandem mass spectrometry was also developed. In sebum, we report for the first time unusual straight-chain polyunsaturated fatty acid isomers (n18:2n-7, n18:2n-3, n20:2n-12, and n20:2n-7), a series of previously unreported branched-chain saturated fatty acids with C19–C26, and a novel branched-chain monounsaturated fatty acid i15:1n-9. A total of 64 fatty acids were identified, exceeding the previous reports. Our study established a comprehensive qualitative and quantitative workflow for the analysis of sebum fatty acids and squalene, with the potential to advance dermatological research and clinical diagnostics.