Hair Lipid Structure: Effect of Surfactants

Human hair fibres are mainly comprised of proteins (>90%) and lipids (1–9%), which are characterised as exogenous or endogenous, depending on whether they originate from sebaceous glands or hair matrix cells, respectively. Exogenous lipids consist of free fatty acids (FFAs), triglycerides, cholesterol (CH), wax esters, and squalene. Endogenous hair lipids comprise FFAs, CH, ceramides, glycosylceramides, cholesterol sulfate, and 18-methyleicosanoic acid. Lipids were demonstrated to be fundamental against damage and maintenance of healthy hair. Several studies have evaluated the effects of hair lipid content and have shown how hair properties were altered when lipids were removed by solvent extraction. The effect of surfactants on hair lipids is difficult to determine, as the complex structure of the cell membrane complex makes it difficult to determine where surfactants act. Shampoos and conditioners contain surfactants that remove lipids during routine cleansing of hair. However, shampooing does not completely remove all free lipids from the surface layers. The effect of surfactants on the alteration and removal of structural lipids is poorly developed, and there is no consensus on the results. Further research on the lipid composition of the hair could provide information on the penetration pathways of surfactants to improve effectiveness and limit possible damage.