The stratum corneum water content and natural moisturization factor composition evolve with age and depend on body site

BACKGROUND The study objective was to examine if age and chronic environmental exposure affect the water content and the composition of the natural moisturizing factors (NMFs) of the stratum corneum (SC). METHODS Forty healthy Caucasian women 18-70 years of age were recruited. Measurements were done on the cheek and on two skin sites on the arm (one relatively protected and one exposed to environmental factors). SC water content and NMF composition were measured by Raman confocal microspectroscopy. RESULTS The SC water content was gradually reduced with age, reaching statistically significant levels only on the exposed arm site. The SC water content remained higher on the face than on the two arm sites throughout the ages tested. The age-dependent concentration changes of various amino acids were species-specific, potentially indicating different protein sources. Interestingly, on the arm sites, the sum of decreasing amino acid concentrations is compensated by the sum of those increasing, resulting in constant total amino acid content. However, on the face, the total amino acid content statistically increased with age potentially relating to the declining cell turnover rates. The lactate content was higher on the face for all ages and statistically decreased on both arm sites. CONCLUSION Both chronological aging and chronic exposure to environmental factors mildly affect SC hydration, while they have variable effects in the concentrations of NMF components. The dynamics of NMF composition may at least partially explain the age-related changes in SC hydration.