Effect of occlusion on the percutaneous penetration of linoleic acid and glycerol

The effect of occlusion on the in vitro percutaneous absorption of linoleic acid was investigated. A greater skin concentration of linoleic acid from an ethanolic vehicle was observed in non-occluded experiments compared with occluded experiments (P<0.05). Such changes were not observed as consistently when ethanol was replaced with a less volatile organic solvent (cyclomethicone). These observations were attributed to the increase in the concentration gradient due to the unimpeded evaporation of volatile solvents, which provided a greater driving force and enhanced non-occluded delivery in these systems, compared with occluded systems. Conversely, the percutaneous absorption of a polar material (glycerol) from an aqueous solution did not yield any such differences. While more conclusive comparisons between volatile and non-volatile solvents and penetrants would be required to substantiate fully these comparisons, it is apparent that non-occlusion of volatile solvents may enhance percutaneous absorption. The physicochemical properties of the penetrant, for example its natural state at skin temperature (i.e. solid or liquid) may further determine the degree of enhanced percutaneous absorption compared with occluded environments