Skin penetration flux and lag-time of steroids across hydrated and dehydrated human skin in vitro

To study the effect of hydration on skin absorption, we investigated penetration across human skin of twelve model chemicals having steroidal structure but different molecular weight and compared the steady-state penetration rate (J) and lag-time (t) across hydration intact skin (J(h) and t(h)) with that across dehydrated intact skin (J(d) and t(d)). Stratum corneum (SC) thickness of hydrated (52 mu m) is 3.3 times that of dehydrated skin (16 mu m). Transepidermal water loss (TEWL) of hydrated (7.6 +/- 2.1 g/m(2)/h) is twice that of dehydrated skin (3.4 +/- 1.6g/mZ/h,p < 0.05) which are similar to in vivo values, suggesting the SC barrier function was recovered. The ratio of J(h)/J(d) ranged between 0.7 and 3.6 (average of 1.9). On the other hand, the ratio of t(h)/t(d) was almost constant (average of 0.8). Ratios of J(h)/J(d) and t(h)/t(d) were independent of MW and K-o/w. In percutaneous absorption experiments in vitro, skin was preserved in culture medium until use and SC might swell during that time. Therefore, we consider the possibility that J and t varied between hydrated and dehydrated skin. We confirmed the difference of J and t between hydrated and dehydrated skin in vitro and now need to define these results under in vivo condition.