Leviticus 15 prohibits sexual intercourse during menstruation for seven days, and in case of unusually heavy or prolonged menstruation, which suggests illness—for seven days after it has ended. Both prohibitions are entirely separate, with a complete set of instructions for male and female for each prohibition. The two prohibitions are drastically different in terms of how violating them incurrs impurity: regular menstruation, while formally a bleeding, poses no threat to life and doesn’t substantially defile. Men and women alike need only wait a specified period (one and seven days after initial contamination, respectively) to become clean automatically. Not so with unusual, life-threatening bleeding: it incurs a major impurity. Not only does the Torah prescribe an additional seven-day purification period, but the woman must bring sacrifices both to cleanse herself of ritual impurity and to give thanks for healing. Sacrifices are only prescribed for cases of heavy bleeding: it was impractical to require women to travel to the Temple monthly to offer sacrifices after every trivial menstruation. Rabbis twisted that commonsensical rule to ban intercourse for seven days after the end of any menstruation. That greatly inconvenienced observant Jewish couples, robbing them of one week of sexual enjoyment per month. A story asserts that a medieval rabbi introduced the additional five days at women’s demand. Such a demand is unlikely, acting on it is wrong, and adhering to that medieval rule is ludicrous. The truth is surely that the rabbis originally calculated seven days after the end of menstruation—a rule which the Torah intends only for heavy bleeding—but realized that abandoning sex until the fifteenth (or considering the mikvah procedure, often the sixteenth) days greatly reduced the chances for childbearing. They then arbitrarily reduced the term to five days, and invented the explanation.
The requirement of mikvah after menstruation is a rabbinical invention which evolved into an unhealthy rite. Two thousand years ago a requirement of monthly washing was perhaps practical, but asking modern women to immerse themselves in barely warm water—which, moreover, is not treated against bacteria—is absurd. The Torah elaborates on niddah rites, but says nothing about post-menstrual washing for women. Men are required to wash after touching a menstruating woman, but nothing is said about mikvah. Any thorough washing, which is what is meant by the Hebrew root rhtz, would do. The Torah is not a hygiene manual. There are plenty of useful habits not detailed in the book. The Torah deals with ritual, symbolic purity. Rabbis are wrong to elevate useful rites to the rank of commandments. They arbitrarily invent strictures, like the obligation of mikvah. And on the other hand, rabbis released important proscriptions, such as that of a menstruating woman’s seat. The Torah states unequivocally that anything which a menstruating woman uses for a seat is rendered impure. That created an inconvenience for synagogue attendance, and rabbis abrogated the commandment. Their reasoning reduces the Torah to a hygienic manual: in antiquity, menstruating women left bloody traces, while now they don’t. The reasoning behind the prohibition was not hygienic, but ritual; it was a matter of symbolic impurity—to which Tampax is irrelevant.