Lipidomics analysis of facial skin surface lipids between forehead and cheek: Association between lipidome, TEWL, and pH.

Regional differences in skin characteristics are well known. Significant differences in skin physiology between the forehead and cheek have also been reported. However, there are few studies based on lipidomics at the molecular level. Additionally, there is no study focusing on the lipid profile variations of skin surface lipid (SSL) in forehead and cheek.This study analyzed the differences in facial SSL between forehead and cheek of men aged 18-25 years to explain the distinct physiological parameters between forehead and cheek resulting in different skin status.Facial SSL was identified by ultra-performance liquid chromatography-quadrupole time of flight-mass spectrometry (UPLC-QTOF-MS). Multivariate data analysis was used to investigate the SSL difference in forehead and cheek.Significant differences in facial SSL composition were detected between the forehead and cheek. Multivariate data analysis suggested that 21 entities contributed most significantly toward the discrimination and phosphatidylserines (PS) constituted the majority of differentiating lipid species. Subsequent analysis showed a marked increase in the amounts of unsaturated and saturated free fatty acids (FFAs), and a significant increase in average FFAs chain length in the forehead as compared to that in the cheek.Phosphatidylserines exposure might be one of the most important reasons for the increased amount of forehead SSL secretion. The different FFAs chain length and FFAs content lead to altered skin barrier functions in forehead and cheek, consequently resulting in altered trans-epidermal water loss (TEWL) and pH at the two anatomical sites.