Most couples who are interested in keeping the laws of niddah take classes or private lessons to learn all of the details. This article does not replace such a class, but includes the main topics that would be covered in a class about the laws of niddah.
A woman halakhically becomes a niddah, a menstruating woman, if she is experiencing the full flow of her period, or any time she sees red blood emerging from her body or on white underwear that she is wearing, unless she has good reason to believe that the bleeding is not uterine in origin.
According to the Bible, sexual relations are forbidden while a woman is a niddah, and the rabbis prescribe a number of additional regulations. The main ones are avoiding physical contact between spouses and sleeping in separate beds. Many couples also avoid passing objects directly to each other, seeing each other undress, and flirtatious conversation.
Niddah, Yoledet, & Zavah
The Torah distinguishes between niddah, a woman having her regular menstrual period, yoledet, a woman giving birth (which includes a woman having a late miscarriage), and zavah, a woman experiencing an irregular flow of blood. According to the Torah, a niddah simply counts seven days from the first day of her period (including the first day) and then goes to the mikveh to purify herself on the night following the seventh day. Similarly, a yoledet simply counts seven days from the birth of a son or 14 days from the birth of a daughter before going to the mikveh. But a zavah must wait seven clean days after her blood flow has ended before undergoing purification.
The rabbis record that during the time of the Talmud the distinction between niddah and zavah became too difficult to uphold. In order to be on the safe side, all women who experience uterine bleeding are considered to possibly be a zavah. Some talmudic passages attribute this strictness to the women themselves:
“The Israelite women were stringent upon themselves so that even if they see one drop of blood the size of a mustard seed, they wait seven clean days after it (Babylonian Talmud, Berakhot 31a).”