Niacinamide and its impact on stratum corneum hydration and structure.

Summary

Using SAXS/WAXD and dynamic vapor sorption under controlled humidity, the authors show that niacinamide increases SC water uptake at high RH and swells keratin monomer spacing at low RH, indicating a plasticizing effect. It differentially alters lipid matrix diffraction intensities at 60% vs 95% RH, suggesting modulation of water distribution between lipid and protein domains.

Key Findings

• Niacinamide is non-hygroscopic yet increases stratum corneum water uptake at 95% RH.
• At 60% RH, niacinamide swells keratin monomer spacing without increasing bulk water content, indicating a plasticizing effect.
• Niacinamide alters lipid matrix diffraction intensities differently at low versus high RH, suggesting modified water distribution between lipid and protein domains.

Clinical Implications

Formulators can leverage niacinamide’s plasticizing effect to improve flexibility in dry skin and increase moisture retention at high RH; clinicians should recognize it is not a keratolytic and tailor recommendations by climate.

Limitations

• Ex vivo study without in vivo clinical endpoints or barrier function measures.
• Sample donor variability and limited exploration of concentration–response beyond a threshold effect.

Future Directions

Link structural changes to clinical outcomes (hydration, elasticity, TEWL) in randomized trials, map dose–response across broader concentrations, and study interactions with common co-actives.