Characterization of circadian human facial surface lipid composition.
The circadian rhythm is an endogenous clock that governs a wide range of physiological functions. In the skin, rhythmic changes in skin barrier function have been investigated at the physiological level; however, few studies at the molecular level have been reported. Additionally, there is no study on lipidomic profile variations of skin surface lipid (SSL), which could potentially explain the rhythmic changes in skin status. The SSL profile of healthy young women was analysed to assess SSL variations and to assess the skin status during the circadian cycle. Ultra performance liquid chromatography/quadrupole time-of-flight mass spectrometry and multivariate data analysis were performed to assess SSL variations. The lipidomic profile showed significant differences with the circadian rhythm. Multivariate data analysis indicated that glycerolipids were the lipids majorly affected by the circadian rhythm. Additionally, in the SSL profile, both the average chain length and the content of free fatty acids (FFAs) were higher at 20:00 than at 08:00. The SSL profile significantly varied with respect to the circadian rhythm. The rhythm-altered triacylglycerol level, FFA chain length and FFA content resulted in rhythmic changes in skin barrier function, including transepidermal water loss alteration and pH variation.