Biol. Pharm. Bull. 29(11) 2270—2273 (2006)

and underlayed viable epidermis and dermis. Because the SC is highly lipophilic, dry and a relatively effective percutaneous barrier, skin penetration is influenced by physicochemical properties of compounds. Hydrophobic compounds penetrate more easier than hydrophilics and lower than high molecular weight. Relationships between penetration flux and physicochemical properties include: lipophilicity, melting point, molecular weight, and pH of skin and vehicle. Water content of SC is 30 to 50% (w/w) of SC dry weight in vivo and is varied when occluded by a water impermeable membrane and stored into water (e.g. phosphate buffered saline) to be used to skin transplantation and percutaneous absorption experiments in vitro. Increasing SC hydration alters barrier function, hence often increasing percutaneous absorption in vitro. Bucks and Maibach, reporting the effect of occlusion on percutaneous absorption in human in vivo, discussed that the skin occlusion caused SC hydration did not necessarily increase percutaneous absorption of hydrophilic compounds. Thus, the SC hydration is a important factor to reveal the in vivo/in vitro correlation of percutaneous absorption. This study investigated a procedure to prepare dehydrated skin from hydrated skin stored in culture medium for some days and the effect of skin hydration on skin penetration of twelve steroids as model chemicals because they had a similar basic structure and different molecular weight.