Twelve-point scale grading system of scanning electron microscopic examination to investigate subtle changes in damaged hair surface

Background: To assess the hair surface condition, scanning electron microscope (SEM) is commonly used and it remains an indispensable hair morphology characterization technique. Yet, the technique is criticized for having subjective viewpoints and limitations in distinguishing the appearance of cuticle layers. Objectives: The aim of this study is to establish an objective classification system and also to subdivide by detailed description of damaged cuticle layers. Methods: Hair samples were collected from female subjects (n = 500) who participated in hair efficacy study and Asian hair bunches (n = 180) that were previously collected. Damage to hair was initiated by chemical, heat stress and ultraviolet irradiation. We suggested the grading criterion on a 12-point scale and compared with a wide range grading system on a 5-point scale. We evaluated other hair surface-related parameters such as hair luster-ring and combing load to verify the validity and efficacy of our new grading system. Results: The grading criterion on our 12-point scale revealed an improved discrimination compared to the wide range grading system. Hair surface-related parameters were significantly improved after hair care product, and these tendencies were likely to be determined to be similarly improved using the 12-point scale grading system. Conclusion: The 12-point scale classification system was demonstrated to be a more precise standardization and appropriate evaluation method to investigate the subtle distinction of the hair shaft after hair care product application.