Many Jewish women today are reclaiming and refashioning traditional Jewish laws about menstruation, from menarche to menopause to mikvah immersion. Yet menstruation still remains mostly private — a woman is not compelled to disclose to others whether or not she has her period. So it is surprising to learn that among Karaite Jews, who observe Jewish practices as they are literally written in the Torah, woman’s menstrual status is an open secret, and can affect everything from where she can eat and sleep to her participation in Jewish communal practices and rituals.

In The Stains of Culture: An Ethno- Reading of Karaite Jewish Women (Wayne State University Press, $27.95) Ruth Tsoffar, an Israeli-born anthropologist, studies how San Francisco’s Karaite Jews, who emigrated from Egypt (some via Israel), observe biblical menstrual laws in ways that are extremely socially limiting for women.

When a girl first gets her period, she must wash all her clothes, sleep in a separate bed (if she has shared one with a sibling) and eat at a separate table with silverware specifically designated for the menstruating woman or girl. In Karaite communities in Cairo, menstruating women were not allowed to cook food, enter the synagogue or touch anyone, especially their husbands. On the other hand, Karaite couples resume sexual relations seven or eight days after menstruation (a week earlier than the rabbinic tradition mandated), and Karaite women do not immerse in a mikvah after their periods. Instead, they perform a ritual at home in the shower; the woman stands, and another woman pours seven cups of water over her while instructing her to recite the Sh’ma.

Karaite women have the double burden of both hiding and exposing their menstrual status. As one woman ruefully explained, “I grew up in a home in which no one knew that I had my period and when I had my period. But once I got married, I had to tell the whole world that I have my period.” A mother of a bar mitzvah boy is unable to participate in his celebration when she gets her period, even after carefully choosing the bar mitzvah date after long calculations. Another woman who has her period on the first night of Passover must spend the Seder sitting at a separate table, away from her family and other guests. And a Karaite religious teacher once asked one of Tsoffar’s colleagues, “Mah ha-matsav shelakh?” (How is your situation/condition?), and then explained, “It’s not shameful [to be menstruating or to ask about it]. It’s natural. If you have it, we should wash the chair afterwards.”

For all the oppressiveness of these restrictions, they also enable Karaite women to feel connected to generations of women in their community, following rules and codes passed on from mother to daughter. In sharing their stories with us as well, Tsoffar acknowledges that she may make some readers squeamish. Yet by airing Karaite women’s dirty (or bloody) laundry, so to speak, she has opened a window into women’s ritual life in a little-known Jewish community.

Susan Sapiro works for an executive search firm.