Niddah 66: The Menstrual Cycle and Extra Stringencies

Rabbi Zeira says that Jewish women are stringent regarding menstrual blood.  That means that instead of just being ritually impure for the seven days of their periods, they are ritually impure as a zava for an additional week.  Certainly the extra days are an extreme stringency but our tradition insists that women are considered to be ritually impure at least two weeks of each menstrual cycle.