Abstract
BACKGROUND: Circadian rhythms are driven by the biological clock, an endogenous oscillator that generates approximately 24 h cycles in mammals. The circadian regulation of the lipid metabolism plays a crucial role in overall metabolic health. An analysis of the correlation between the skin's physiological parameters and skin lipids can provide a better insight into the rhythmic changes in skin condition. OBJECTIVES: The aim was to reveal how skin surface lipids (SSLs) participate in the regulation of circadian rhythms in the skin and the importance of the circadian oscillation of facial lipid molecules in maintaining epidermal homeostasis. METHODS: Changes in SSLs were assessed using UPLC-QTOF-MS. The skin's physiological parameters were quantified using non-invasive instruments. Multivariate data analysis was employed to evaluate the differences. RESULTS: Both skin surface lipids and physiological parameters exhibited certain circadian variation patterns. Four major lipid classes (fatty acids, glycerophospholipids, prenol lipids, saccharolipids) exhibited circadian rhythmic trends, with seven lipid subclasses contributing most significantly to the overall patterns observed. Among the physiological parameters assessed, sebum secretion, transepidermal water loss, moisture measurement value, and skin surface temperature exhibited sinusoidal circadian rhythms. Further analysis revealed significant correlations between fatty acids and saccharolipids with moisture measurement values, and between glycerolipids and pH value. In addition, lipids closely associated with the barrier such as unsaturated fatty acids and ceramide chain lengths correlated significantly with moisture measurement values. CONCLUSIONS: Through correlation analysis, the study elucidates the influence of diurnal fluctuations in skin surface lipids on skin barrier function. These findings hold significant implications for understanding skin barrier impairment associated with circadian rhythm disruptions.