Zesch A, Schaefer H, Stüttgen G
Arch Dermatol Res. 1979 Nov;266(3):277-283. doi: 10.1007/BF00418573.
The distribution coefficient of caffeine (water/n-Octanol) and the estimation of caffeine in urine after local application indicate to a high permeation rate of caffeine through the skin. This could be confirmed by using different vehicles in vivo and in vitro. 14C labeled caffeine penetrates rapidly the epidermis and corium. The maximum of absorption is reached at 100 min after local application in vivo. In vitro by absence of the transport possibilities of blood and lymph vessels, the concentration at 1,000 min after local application is 450 X higher than in vivo. Therefore, after 1,000 min in vivo the concentration of caffeine in the different skin layers is very low.
咖啡因的分配系数（水/正辛醇）以及局部应用后尿液中咖啡因的含量估计表明，咖啡因经皮肤的渗透速率很高。这一点可通过在体内和体外使用不同载体得到证实。14C标记的咖啡因能迅速穿透表皮和真皮。在体内局部应用后100分钟达到吸收最大值。在体外，由于不存在血液和淋巴管的转运可能性，局部应用1000分钟后的浓度比体内高450倍。因此，在体内1000分钟后，不同皮肤层中咖啡因的浓度非常低。
