Background: Preterm infants have immature skin, which contributes to skin problems. Very little is known about postnatal changes in the skin, despite the clinical importance of this issue. Aim: To assess temporal changes in skin water content in preterm infants. Study design: A prospective observational study. Subjects: Infants admitted to the neonatal intensive care unit were included in this study. Outcome measures: Skin water content was measured at five different skin regions using dielectric methods at a depth of 1.5 mm. Skin water content was measured on postnatal day I in 101 infants, and the correlation between skin water content and gestational week was analyzed. Measurements were also made on postnatal days 2,3, and 7, and every 7 days thereafter until the corrected age of 37 weeks in 87 of the 101 infants. Temporal changes were statistically analyzed after dividing participants into seven groups by gestational age. Results: On postnatal day 1, skin water content correlated inversely with gestational age at all skin regions. Skin water content decreased significantly over time, converging to the level of term infants by the corrected age of 32-35 weeks. Conclusions: Skin water content at a depth of 1.5 mm was related to corrected age and reached the level of term infants by the corrected age of approximately 32-35 weeks. (C) 2015 Elsevier Ireland Ltd. All rights reserved.