The stratum corneum (SC) serves as the skin’s primary barrier, protecting against harmful substances and minimizing water loss. Niacinamide (NIA), a form of vitamin B3, is a popular skincare ingredient known for its safety and efficacy in treating various skin conditions. While NIA’s anti-aging and skin- Hydration benefits are well-documented, its direct impact on the SC’s hydration and molecular organization remains unclear. This study addresses this gap by examining how NIA influences the SC’s lipid matrix organization, soft keratin structure, and water sorption behavior at different humidity levels.
Methods
The study used small- and wide-angle X-ray diffraction (SAXD and WAXD) and dynamic vapor sorption (DVS) to compare NIA-treated SC samples with untreated controls under varying relative humidity (RH) levels. SC samples were pretreated with acidic and neutral buffers, with and without salt, and incubated with 5 wt% NIA for 24 hours. The structural organization of the SC and its hydration process were then analyzed.
Key Findings
•Hydration Properties: NIA enhances water uptake of the SC at high humidity (95% RH) but is non-hygroscopic itself1…. At low humidity (60% RH), NIA slightly reduces SC water content.
•Keratin Structure: NIA swells the keratin monomer spacing at low humidity (60% RH), suggesting a plasticizing effect that could increase SC flexibility in dry conditions. This effect is similar to that of water, but occurs even when the SC water content is low.
•Lipid Matrix Organization: NIA modifies diffraction intensities from the lipid matrix differently at 60% and 95% RH, indicating it interacts with the SC lipid matrix and influences water distribution within the lipid and protein domains. Hydration of the SC generally intensifies diffraction profiles from the lipid matrix, but NIA modifies this effect.
•Concentration Threshold: The effects of NIA appear independent of the dose regime, indicating a specific concentration threshold.
•pH and Salinity: The effects of NIA were not influenced by the salinity or pH of the pretreatment media.
This research provides novel insights into how NIA interacts with the SC. The study demonstrates that NIA enhances water uptake at high humidity and swells keratin monomer spacing in dry conditions, suggesting it acts as a plasticizer. Moreover, NIA’s interactions with the lipid matrix and its influence on water distribution within the SC highlight its complex role in maintaining skin hydration and flexibility. This study is significant because it elucidates the biophysical mechanisms underlying NIA’s beneficial effects on the skin barrier, with potential implications for developing more effective skincare formulations. Future research could explore how these molecular-level changes translate into macroscopic improvements in skin health and the optimization of topical formulations containing NIA.
Link to the study: https://www.nature.com/articles/s41598-025-88899-0
