A study of the volume and bounce decrease in hair with aging using bending elasticity measurements

Hair diameters and bending stresses were measured for chemically untreated regions of hair close to the scalp, collected from 38 Japanese female (age range: 26 to 51) and 35 Caucasian female (age range: 20 to 40) volunteers. For the bending stress measurements, a new methodology to obtain averaged Young's modulus has been developed in which 50 fibers are measured together to give reproducible data, overcoming the individual differences in each hair fiber. By comparing the resulting data of the fibers collected from the panelists younger than 40 years of age, no significant difference in Young's modulus between Japanese and Caucasian hair was recognized, and the modulus was ca. 10 GPa, regardless of the hair diameter. On the other hand, there existed cases in which fibers showed lower Young's moduli, and these fibers were from senior panelists who were conscious of the decrease in hair volume and bounce with aging. This result indicates that the decrease in volume and bounce in hair with aging is not only caused by a decrease in hair diameter and fewer hairs per square centimeter of scalp but also by some internal change in the hair.