Loss of colour or greying of hair is a phenomenon related to ageing and is one of its most obvious signs [1]. The loss of melanin not only produces a loss of colour but also has relevance to hair’s hygroscopic character and its affinity for metals [2]. Knowledge of hair’s properties has usually been related to the hair’s protein fraction. However, recently the importance of the lipid part of the hair fibre has become apparent [3]. During age‐related loss of colour, the lipid composition of hair may also be altered at the same time that its melanin content decreases, which may lead to a modification of the fibre properties. The main objective of this study was to determine the lipid profile of brown and white Caucasian hair fibres and the effects of lipids on the properties of fibres. Extractions of exogenous and endogenous lipids with different organic solvents and their analysis by thin-layer chromatography coupled to an automated flame ionization detector were carried out. Lipid extracts thermotropic behavior was determined using different techniques such as differential scanning microscopy and thermogravimetric analyses. To determine the structures of white and brown hair lipid bilayers, cross sections of fibres of both hair types were examined using synchrotron‐based μ‐FTIR mapping. Dynamic vapour sorption analyses were also performed to determine the differences in the barrier function of both fibres. Lipids analyses showed the highest amount of lipids for the brown hair fibres. Besides, the aged related loss of colour of the white hair fibres involves a loss of hair lipids saturations demonstrated by decreased values of transition and degradation temperatures in the differential scanning calorimetric and thermogravimetric analyses, respectively. Spatial identification of lipids showed that brown hair possesses a greater amount of lipids in the medulla and the cuticle. The cuticle of a white hair fibre showed a significant decrease in its lipid content, but did not show differences in the lateral packing order with respect to the cuticle of a brown hair fibre. The cortex and medulla of the white hair fibre also exhibited a significant decrease in its lipid content but with a higher lateral packing order than brown hair. Using DVS analysis, it was found that the water dynamics of white hair fibres differed from those of brown hair fibres, showing a decrease in their total capacity to absorb water and an increase in the velocity of the exchange of water with the environment. The different hair properties due to lipid content indicate a special need of lipid formulation for white hair.
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[2] Hong L, Simon JD. Current understanding of the binding sites, capacity, affinity, and biological significance of metals in melanin. J Phys Chem B. 2007;111:7938‐7947.
[3] Martí M, Barba C, Manich AM, Rubio L, Alonso C, Coderch L. The influence of hair lipids in ethnic hair properties. Int J Cosmet Sci. 2016;38(1):77‐84.