Effect of human skin storage on stratum corneum drug penetration assessed by confocal Raman spectroscopy.

1. Int J Pharm. 2026 Oct 16;706:127563. doi: 10.1016/j.ijpharm.2026.127563. Online ahead of print. Effect of human skin storage on stratum corneum drug penetration assessed by confocal Raman spectroscopy. Schmolz J(1), Cerbu D(2), Barker S(3), Freystätter C(4), Elbe-Bürger A(2), Klang V(5). Author information: (1)Department of Pharmaceutical Sciences, University of Vienna, Josef-Holaubek-Platz 2, Vienna, 1090, Austria; Vienna Doctoral School of Pharmaceutical, Nutritional and Sport Sciences, University of Vienna, Josef-Holaubek-Platz 2, Vienna, 1090, Austria. (2)Department of Dermatology, Medical University of Vienna, Währinger Gürtel 18-20, Vienna, 1090, Austria. (3)Department of Pharmaceutical Sciences, University of Vienna, Josef-Holaubek-Platz 2, Vienna, 1090, Austria. (4)Department of Plastic, Reconstructive and Aesthetic Surgery, Medical University of Vienna, Währinger Gürtel 18-20, Vienna, 1090, Austria. (5)Department of Pharmaceutical Sciences, University of Vienna, Josef-Holaubek-Platz 2, Vienna, 1090, Austria. Electronic address: victoria.klang@univie.ac.at. Fresh human skin is the preferred model for ex vivo dermal penetration studies. However, limited availability often necessitates frozen storage. We investigated whether storage for two months at -20 °C or -80 °C affects skin barrier function, selected Raman-derived skin properties, and drug penetration. For each of six donors, paired full-thickness abdominal skin samples were analyzed fresh or after frozen storage. Barrier integrity was assessed by transepidermal water loss, while quantitative confocal Raman spectroscopy was used to determine water concentration profiles and the amount of caffeine, diclofenac sodium, and salicylic acid within the upper 15 µm after application of 2% (w/w) hydrogels for 1 h. Transepidermal water loss varied across storage conditions, although neither frozen-storage condition differed significantly from fresh skin. Raman-derived water content was significantly higher after storage at -80 °C than in fresh or -20 °C-stored skin, whereas no consistent storage-related differences were detected in the fingerprint spectra or combined ceramide and fatty acid signal. Superficial caffeine uptake was 18.57, 19.82, and 21.51 µg/cm2 in fresh, -20 °C-stored, and -80 °C-stored skin, respectively, with significantly higher uptake in -80 °C-stored skin than in fresh skin. No significant differences were detected for diclofenac sodium or salicylic acid. Under these conditions, storage at -20 °C did not significantly alter the Raman-derived stratum corneum parameters or superficial drug uptake outcomes, whereas storage at -80 °C altered the superficial Raman-derived water signal and caffeine uptake. Storage conditions should therefore be standardized for each compound and experimental endpoint. Copyright © 2026 The Authors. Published by Elsevier B.V. All rights reserved. DOI: 10.1016/j.ijpharm.2026.127563 PMID: 42887571 Conflict of interest statement: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.