Furthermore, we sought to clarify one of the mechanisms by which skin penetration of SG with O/W emulsions increases
more than when the oil vehicle is used. The influence of skin hydration on the skin penetration of DiI by using an oil suspension of DiI and water was assessed. YMP skin was pretreated with water before the application of a DiI suspension.
Figure 5 shows CLSM images of cross-sections of YMP skin after the application of a DiI suspension (a) and a DiI
suspension with water pretreatment (b). The amount of DiI that penetrated the skin after pretreatment with water was
more than that after application of a DiI suspension alone. This indicated that hydration of the skin increases the skin
penetration of DiI.
In our previous study, the skin penetration of SG was enhanced using oils with lower molecular weights and low surface tension as a vehicle.11) The skin penetration order of SG in O/W emulsions in the present study was similar to that
observed in our previous study. Other explanations include that the skin penetration of compounds was affected by hydration of the stratum corneum.12) Our results indicate that the skin penetration of SG in O/W emulsions is affected by both hydration and physical properties of the oil phase.
In the present study, we evaluated the skin penetration of SG and DiI applied in O/W emulsions and under finite dose conditions. The amount of SG skin penetration was greater for
the O/W-type emulsions than for the oil-phase preparations. Furthermore, skin penetration with the oil phase increased on
using oils with lower molecular weights. We conclude that the extent of SG skin penetration can be enhanced using O/W-type emulsions containing LP with a low molecular weight.