The present invention provides a substance which promotes the transdermal absorption of a pharmacologically active component while little irritating the skin. The present invention relates to a transdermal absorption promoter which comprises, as the active component, at least one member selected from among isopulegol, 2-(menthoxy)ethanol and 2-methyl-3-(menthoxy)propane-1,2-diol and an external skin formulation which comprises a pharmacologically active component such as a psychotropic component, an anti-inflammatory component, an analgesic component, an antipyretic component, a whitening component or a hair growth-promoting component, together with the aforesaid transdermal absorption promoter.
