This term, first used by medieval commentators (see Zimmerman, p. 27, note 6), is, itself, an inaccuracy: Rabbi Zera merely describes a stringent practice which Babylonian Jewish women had taken upon themselves. Thus, the correct term should be ḥumra divnot Yisrael, “the stringency of the daughters of Israel,” or, as the Talmud itself describes it, minhaga, “custom.” Yaakov Elman suggests that the stringency of the Babylonian women in this matter is rooted in the extreme aversion to menstrual impurity found in the dominant Zoroastrian religion of their neighbors….
Moshe Benovitz, “A Lifetime Companion to the Laws of Jewish Family Life and Man and Woman: Guidance for Newlyweds (review),” Nashim: A Journal of Jewish Women’s Studies & Gender Issues vol. 12, no. 1 (2006), 326, n. 15.