The aim of this study is to characterize the ability of multiphoton microscopy in monitoring the
transdermal penetration enhancing effect of a depilatory agent and the associated structural
alterations of stratum corneum. The result is compared with the electron microscopic findings. Our
results show that the penetration of both hydrophilic and hydrophobic agents can be enhanced. The
morphology of corneocytes becomes a homogenized pattern with focal detachment of surface
corneocytes. In combination with Nile red staining, multiphoton imaging also shows that the regular
motar-like distribution of lipid matrix was disrupted into a homogenized pattern of lipid distribution.
These results are well correlated with the findings of ultrastructural analysis by electron micrographs
showing disintegration of the protein envelope of coenocytes, disruption of intracellular keratin and
loss of the regular lamellar packing of intercellular lipids. We conclude that, in addition to
quantifying the permeation profiles of model drugs, multiphoton microscopy is able to detect the
penetration enhancer-induced structural alterations of stratum corneum.