Abstract Recently, the PIT (phase-inversion-temperature) system was originated and developed by Shinoda and his collaborators as a guide to surfactant selection. In order to apply the PIT system to the cosmetic field, the effects of various factors on the PIT have been reinvestigated using cosmetic materials. POE alkyl ethers, whose distribution of EO chain lengths is broad, are widely used in cosmetics. In such a case, the effect of the distribution of the EO chain lengths is important. When a surfactant with a distribution of EO chain lengths was used, the PIT was lowered by an increase in the concentration of the surfactant, but when a monodisperse surfactant without any distribution was used, the PIT scarcely varied with the concentration of the surfactant. In the case of the surfactant with a distribution of EO chain lengths, however, if the ratio of oil to surfactant was kept constant, the PIT scarcely varied with the ratio of oil phase to water phase. This relationship can be used in estimating the PIT in the case of the practical production of an emulsion.