Multimodal Evidence of Mesostructured Calcium Fatty Acid Deposits in Human Hair and Their Role on Hair Properties

The document presented the first definitive evidence of exogenous calcium fatty acid deposits in human hair, which accumulate between the cuticle layers and can grow large enough to alter the hair's optical and mechanical properties. These deposits were analyzed using various spatially resolved techniques, including synchrotron micro X-ray fluorescence, X-ray scattering, focused ion beam-scanning electron microscopy, scanning transmission electron microscopy, X-ray energy dispersive spectroscopy, and Fourier transform infrared and Raman imaging. The analyses indicated that the deposits are mesostructured and consist of calcium C16/C18 saturated fatty acids, likely originating from natural sources like sebum. Additionally, X-ray microtomography and serial "slice and view" FIB/SEM were used to determine the location and three-dimensional shape of these deposits within the hair fiber.