Although more than thirty years of intensive investigation have passed since McClintock first published results on menstrual synchrony, there is still no conclusive evidence for the existence of this phenomenon. Indeed, a growing body of nullresult studies, critiques of menstrual synchrony studies, and the lack of convincing evolutionary explanations bring into question the existence of this phenomenon. This paper presents results of a study conducted over five consecutive months in Polish student dormitories. In 18 pairs and 21 triples of college-age women, menstrual synchrony was not found. Social interactions, considered the most important factor mediating the effect of menstrual synchrony, was unrelated to any difference in menstrual cycle onsets. Initial menstrual onset difference was influenced by woman's body mass and menstrual cycle irregularity. These results provide further evidence that women do not synchronize their menstrual cycles.
Keywords: Menstrual cycle; Menstrual synchrony; Social interactions.