We investigated whether an emulsifier or an emulsified oil affects the skin penetration of stearyl glycyrrhetinate (SG) when it is applied in an oil-in-water (O/W)-type emulsion under finite dose conditions in vitro. SG has a high molecular weight (MW: 723) and high lipophilicity (log P: 15.6). Skin penetration of SG applied with O/W emulsions was evaluated using 6 types of emulsifiers that are commonly used in cosmetics; however, no significant differences were observed between these emulsifiers. When applied with liquid paraffins in oil phase, SG skin penetration increased significantly as the molecular weight of the liquid paraffin decreased. The skin penetration of the fluorescent dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI; MW: 834, log P: 23.2) also increased with O/W-type emulsions containing liquid paraffins of lower molecular weights. These results indicate that use of O/W-type emulsions with an appropriate oil phase can improve SG skin penetration.

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