We aimed to establish screening and efficacy test techniques for use in the development of hair-promoting agents. To this end, we used the dermal papilla cell (DPc)-derived immortalized cell line (SV40T-hTERT DPc) and neonatal foreskin-derived keratinocyte cell line (Ker-CT) to form an immortalized cell-based hair follicle-like structure. The SV40T-hTERT DPc spheroids exhibited a higher cell ratio in the spheroids than primary DPc spheroids, and SV40T-hTERT DPc aggregated with spheroids larger in diameter than primary DPc when the same cell number was seeded into the low-adhesion plate. Microscopic imaging and fluorescence staining results indicated that both primary and immortalized cell combinations form a hair follicle-like structure with a long-stretched keratinocyte layer under the condition that the spheroids have the same diameter as that of in vivo dermal papillary tissue in the hair follicle. The hair follicle-like structure elongation was increased upon treatment with three known hair follicle growth-promoting compounds (minoxidil, tofacitinib, and ascorbic acid) compared with that in the control group. Therefore, using immortalized cells to generate a coherent follicle-like structure, we have developed models for screening and evaluating hair-care materials commonly used in the industry.

Although hair aging affects appearance and hair quality, objective biomarkers linking molecular alterations to clinically relevant mechanical properties of hair remain limited. Here, we investigated the relationships among age, hair tensile resistance, and cortical disulfide bond content. Hair shafts from healthy volunteers (20–40 years vs. > 50 years) were analysed for tensile resistance, which was measured as maximum tensile force, and disulfide bond content was assessed by Raman spectroscopy. In parallel, human scalp hair follicles were stratified according to disulfide bond content and donor age to generate transcriptomic datasets for analysis. We identified follicular gene‐expression signatures associated with these parameters. Differential expression analysis revealed a shared gene set associated with reduced disulfide bond content and age, which was subsequently evaluated in ex vivo human hair follicle cultures. Among these candidates, cochlin ( COCH ) emerged as a prominent candidate gene associated with higher cortical disulfide bond content and enhanced tensile resistance of the hair shaft. Immunohistochemical analysis revealed that COCH predominantly localized to the hair matrix and outer root sheath, supporting a follicle‐derived contribution to shaft biochemistry. Together, these findings identify COCH as a promising candidate marker linked to disulfide bond integrity and tensile properties of human hair and establish an integrative framework for connecting follicular gene expression with age‐associated changes in hair shaft mechanics.