Multiple influences on menstrual synchrony: Kibbutz roommates, their best friends, and their mothers

Menstrual onset dates of women living in kibbutzim were compared with those of their roomates, their best friends in the kibbutz, and their mothers. Since these three groups of women constitute the overwhelming number of the subjects' female interactions, this enabled the examination of multiple influences on menstrual synchrony. Synchrony was found between roommates and between best friends, but not between mothers and daughters. The relationships of friendship and joint activities to synchrony were also analyzed. The findings support a pheromonal, and not an environmental, explanation of menstrual synchrony. © 1993 Wiley‐Liss, Inc.