This paper reviews basic facts on vaginal histology and ultrastructure with respect to
passage of different substances and drugs through the epithelium. Particular interest is
devoted to the action mechanism of topically-applied vaginal estrogen, its binding to
receptors in different vaginal cell types, and possible local metabolic routes. Differences in
estrogen sensitivity between uterus and vagina are discussed as well as the background for
the high vaginal sensitivity.