Objective To systematically investigate whether linoleic acid （LA） can induce a phenotypic shift from nonkeratinized oral mucosa towards a vermillion-like keratinized state. Methods Immunohistochemistry （IHC） was used to compare the expression of region-specific keratinization markers between human lip mucosa and vermillion， establishing phenotypic criteria. Primary human lip mucosal epithelial cells were then isolated and cultured. Cells were treated with LA， and the expression of keratinization markers （e. g.， CK10， Involucrin， Loricrin） was assessed via RT-qPCR， Western blot， and immunofluorescence. To explore the mechanism， an ALOX15 inhibitor was used to verify its necessity and the key LA metabolite 13S-HODE was also introduced. For tissue-level validation， a novel full-thickness ex vivo lip mucosal model was established using a Transwell air-liquid interface （ALI） culture system， followed by morphological and IHC analysis after LA treatment. Results LA treatment significantly upregulated key molecules related to terminal differentiation and barrier formation in lip mucosal epithelial cells， without affecting the oral mucosa-specific SPRR3. This suggests LA drives a “hybrid keratinization program” with both mucosal and epidermal features. Mechanistically， this process likely depends on activating the ALOX15/13SHODE axis. The ex vivo tissue model also confirmed that LA treatment enhanced cornified layer thickness and CK10 deposition， improving epithelial barrier integrity. Conclusion This study provides the first systematic evidence at molecular， cellular， and tissue levels that LA is a key bioactive lipid regulating keratinization and barrier function in oral mucosal epithelium.

Linoleic acid, Lip, Oral mucosa, Epithelium, Keratinization