Rabbi Zeira's stringency (Imperial Aramaic: חומרא דרבי זירא) or the stringency of the daughters of Israel (Hebrew: חומרת בנות ישראל) relates to the law of niddah (a woman during menstruation) and refers to the stringency expounded in the Talmud where all menstruant women, at the conclusion of their menstrual flow, were to count seven days of cleanness, just as women would do who suffered an "irregular flow" (Hebrew: זיבה, romanized: zivah) as defined in Jewish law.
[1] By declaring that all women had the status of zavah gedolah, this required them to count seven days of cleanness before immersing.
[4][5] Laws of a zavah (both major and minor)' pertaining to purity and relations are identical to that of a niddah, the main difference being the duration of the impurity.
Another difference is that a major zavah must bring a special offering of a pair of birds to the temple (Leviticus 15: 29–30).
[6] In effect, this meant that in most cases, women needed seven days of cleanness as part of their purification process after menstruation, long before Rabbi Zeira's stringency came to be.
Following the ordinance, many women took upon themselves to practise seven days of cleanness even if they had experienced a discharge of blood of minuscule amount, even as small as a seed of mustard.
Other cases in which the purification process may be prolonged because of Rabbi Zeira's stringency include impurities due to spotting, stains, or as a result of miscarriage.