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

We provide the first conclusive evidence for the presence of exogenous calcium fatty acid deposits, which not only form in-between the cuticle layers in the lipid-rich cell membrane complex, but also grow to dimensions large enough to cause the structure to bulge, thereby impacting the optical and mechanical properties of the hair fiber. The composition and phase of these deposits were probed using a multimodal analytical approach with spatially resolved techniques including synchrotron micro X-ray fluorescence coupled with X-ray scattering, focused ion beam (FIB)-scanning electron microscopy (SEM), scanning transmission electron microscopy, X-ray energy dispersive spectroscopy, and Fourier transform infrared and Raman imaging where the collective analysis is consistent with a meso-phase composed of calcium C16/C18 saturated fatty acids from natural sources such as sebum. X-ray microtomography and serial "slice and view" FIB/SEM both reveal the location and volumetric shape of the deposits.