The Effect of Graying Process on The Mechanical and Chemical Properties of Human Hair: An Experimental Study

Aging significantly impacts the form and function of the human body. One of the most obvious signs of aging is scalp hair graying which often encourages people to use hair dyes. Investigating the chemical and physical properties of black and white hair could lead to improve the quality of cosmetic products. Therefore, the current study aimed to analyze the changes in the structural, mechanical, and chemical properties of human hair fibers due to the graying process. White and black hair fibers were collected from West-Asian females, and their morphology, chemical structure, and mechanical properties were studied using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and uniaxial tensile tests. The results revealed that the morphological properties of black and white hairs did not significantly differ ($p\gt0.05$). Additionally, FTIR analysis indicated that black hair exhibited a higher peak around $3350 \mathrm{~cm}^{-1}$ compared to white hair, possibly due to melanin content. Furthermore, mechanical tests demonstrated that white hair samples were significantly stiffer that black hair samples $(\boldsymbol{p}\lt0.05)$. Based on these findings, it can be concluded that graying affects the mechanical and chemical properties of human hair fibers. Therefore, considering these differences may contribute to improving the quality of cosmetic products, and provide insights into the mechanobiological aspects of aging.