Quantitative Studies on Human Hair Growth: Fundamental Measurements and Evaluation of Hair Growers

The study conducted quantitative analyses on human hair growth using optical microscopy and image analysis, focusing on regional differences and age-related changes in 14 healthy male subjects and 28 male subjects, respectively. It was found that temporal hairs grew the fastest, while frontal hairs grew the slowest. With aging, there was a significant decrease in hair growth rate, terminal hair density, and hair diameter, particularly in the vertical region, along with an increase in resting or slow-growing hair. In alopecia subjects, hair growth in the vertical region was 50% lower, and the ratio of resting or slow-growing hair was about 3 times higher compared to healthy subjects. The study also evaluated the effects of hair tonics on alopecia subjects over 6 months, finding that the test tonic increased hair growth rate and decreased the ratio of resting or slow-growing hair, whereas the control tonic had the opposite effect.