In this study, we discovered that washing hair with surfactants causes a decrease in the internal density of hair, and we propose a cuticle-sealing strategy to inhibit this phenomenon. This phenomenon was revealed based on optical analyses such as optical microscopy, scanning electron microscopy (SEM), drop shape analysis, atomic force microscopy (AFM), and single hair analysis. Repeated ... [Show full abstract] treatment with surfactants creates areas of low density within the hair. Additionally, treatment with low-molecular-weight materials resulted in replenishment of the internal density of the hair. It has been shown that the more severe the degree of cuticle lifting, the more the internal density of the hair is reduced by surfactants. In addition, the study confirmed that a decrease in internal density could be prevented by sealing the cell membrane complex (CMC), and it was suggested that this reduced internal density may reflect the pore structure of hair. This study investigates the mass transfer phenomenon that occurs in hair and proposes a strategy to maintain hair homeostasis.