Chronological Aging of Human Hair Keratin Fibers

The study examined very long human hair (over 2.4 meters) to understand the natural aging process of hair keratin fibers using various evaluation methods. It found that hair aging begins with the progressive abrasion of the cuticle while the cortex remains unchanged up to about 1 meter from the root, maintaining shine, hydrophobicity, and friction characteristics. Beyond this point, significant cuticle damage occurs, correlating with a decline in ceramides, 18-Methyl Eicosanoic Acid (18-MEA), and keratin-associated protein content. This leads to a noticeable decay in the mechanical and optical properties of the hair. The research provided a detailed time-dependent 'damage scale' of human hair, which could aid in developing new hair care products.