The Effect of Skin Storage Conditions on Drug Permeability

Abstract

In the development of skincare products and topical medications, numerous penetration tests have been performed on both human and animal skin to confirm drug efficacy and safety. Typically, test skin is stored frozen to facilitate distribution and prevent degradation, and is subsequently used after thawing. While many studies have examined the effects of freezing and thawing on skin structure and drug permeability, results vary significantly due to differences in factors such as animal species, freezing temperatures, and durations. As a result, the effects of freezing and thawing on the skin currently remain controversial. In this study, we utilized fresh facia（l eyelid）skin obtained from the same individual immediately post-surgery to investigate the differences in drug permeability between frozen and unfrozen skin. Our findings indicated that the cumulative skin permeability of water-soluble caffeine and oil-soluble isopropylmethylphenol was lower in unfrozen skin compared to frozen skin. No significant difference was observed in esterase activity between frozen and unfrozen skin, suggesting that freezing and thawing may affect the physical barrier function of the skin. Additionally, we considered the concentration of residual drug in the stratum corneum, epidermis, and dermis post-permeation test, as well as the analysis of intercellular lipid structure using confocal Raman spectroscopy.