Oleic acid‐induced interleukin‐36γ: A possible link between facial skin redness and sebum

Background Redness of the facial skin is an important cosmetic concern. Although qualitative and quantitative modifications of sebum on the skin surface are major pathogenic factors of chronic inflammatory skin conditions, the relationship between skin redness, sebum, and mild inflammation on the cheeks of healthy subjects remains elusive. Aims We aimed to explore the correlation between cheek redness and sebum and inflammatory cytokines in the stratum corneum (SC) of healthy subjects. We also examined the effects of representative sebum lipids on the gene expression of inflammatory cytokines in cultured keratinocytes. Patients/Methods This study included 198 healthy participants. Skin sebum was analyzed using flow injection analysis, and skin redness was assessed using a spectrophotometer. Inflammatory cytokines in tape‐stripped SC were measured using enzyme‐linked immunosorbent assay. Results Cheek redness parameters positively correlated with the amount of skin sebum and the proportion of monounsaturated free fatty acids (C16:1 and C18:1) in the sebum. They also positively correlated with the interleukin (IL)‐36γ/IL‐37 ratio in the SC. Among the representative sebum lipids examined, oleic acid (C18:1, cis‐9) dose‐ and time‐dependently regulated the mRNA expression of IL‐36γ and IL‐37 in cultured keratinocytes, and this effect was attenuated by the N‐methyl‐D‐aspartate (NMDA)‐type glutamate receptor antagonist, MK801. Conclusions Skin surface sebum may be related to cheek redness in healthy subjects, and oleic acid‐induced IL‐36γ through NMDA‐type glutamate receptors may be a link between them. Our study provides a possible skincare strategy for mitigating unfavorable increase in skin redness by targeting the facial skin sebum, particularly oleic acid.