KRT27 is a type I keratin essential for assembling keratin intermediate filaments in the inner root sheath (IRS) of hair follicles. 1 It functions as a structural protein critical for hair follicle morphogenesis and epithelial differentiation, with expression patterns in wool follicles suggesting roles in follicle anchoring and morphology determination. 1 KRT27 expression is tightly regulated during the hair growth cycle, with transcription occurring early in anagen and becoming restricted during catagen regression. 1 Clinically, KRT27 serves as a biomarker for hair growth status. Elevated expression correlates with enhanced hair growth promotion in response to collagen peptide supplementation 2 and is suppressed in androgenetic alopecia associated with elevated homocysteine levels. 3 In alopecia areata, KRT27 expression is consistently repressed across disease subtypes, with the strongest reductions in severe forms (alopecia totalis/universalis), suggesting loss of follicular structural integrity contributes to pathology. 4 KRT27 is also expressed in basal cell carcinoma, a hair follicle-derived tumor, where it marks inner root sheath differentiation. 5 Additionally, KRT27 was identified as associated with longer progression-free survival in immunotherapy-treated lung cancer patients, though its mechanistic role in this context remains unclear. 6 These findings establish KRT27 as both a structural component essential for normal hair follicle function and a potential therapeutic target in hair loss disorders.