NUDE RAT SKIN PERMEABILITY 301 100- o o o 7 o m 10 ÷ ] I i i 0 2 4 6 ALKYL CHAIN LENGTH Figure 1. In vitro permeability profile of n-alkanols through nude rat skin. availability to the skin. This is an area which is still being researched at a very basic level and is beyond the scope of this paper. However, it should be noted that the recent in situ data of C. R. Behl et al. (4,9, 10) have shown an absence of the second plateau and a linear rise in the P-values up to decanol. Alkanols higher than decanol were not tested in these studies. A possible explanation for the observed second plateau in the in vitro data may be that permeation of highly lipophilic molecules is retarded by the aqueous tissue control pathway of the viable epidermis/dermis region of the skin. The presence of a blood supply in a living animal (or human) may quickly remove the permeants from the viable epidermis and, thus, may either eliminate or delay the emer-

302 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS o o o x z o -- 200- 100: s MOUSE 100: 1 1 0 i ,b o 100: 100: 10' ._•'•RRY RAT 10' •MOUS 100: 1500- 1000: J i lOO ,,// SILASTIC MEMBRA 80 urn ,ol , 0 5 10 0 5 1•3 ALKYL CHAIN LENGTH Figure 2. In vitro permeability profile of n-alkanols through various animal skins, human skin and Si- lastic © membrane.