Also in this week's column:

• Great moments in human research 2: "Concluding, among other things..."
• What ever happened to tuberculosis?
• What is sexsomnia?

Asked by Linda Phillips of Byron Bay, NSW, Australia

Menstrual blood is seen as dangerous, magical, and even sacred across many religions and cultures. The origin of the taboo against sexual intercourse while a woman is menstruating is probably lost to antiquity. Yet this taboo is found in every corner of the world - from Africa, to Polynesia, to the Plains Indians of North America, and so on.

Classical anthropologist Robert Briffault (1876-1948) in The Making of Humanity (1919) suggested that the Polynesian word tupua or tabu, which comes to us as taboo, actually means both "menstruation" and "sacred". Tabu means "mark especially" in Tongan. Kapu means "sacred, forbidden" in Hawaiian. Tapu means "restricted, sacred" in Tahitian. Tapu means "be under ritual restriction, prohibited" in Maori.

Today, the taboo against sexual intercourse with a menstruating woman is both prominent and debated in the Jewish, Islamic, and Hindu religious traditions, among others.

According to Dr Terri Foran, a sexual health physician from of the School of Women's Health at the University of New South Wales in Sydney, Australia, in pre-Judaic times, women were often isolated in a red tent during their periods and prevented from doing many activities, including engaging in sex.

This isolation occurred because it was believed that menstrual blood would "sap their husband's sexual power". Dr. Foran adds that: "[T]his tradition has little medical basis and is only by aesthetic choice. Having sex during this time harms neither partner, although there is increased risk of transmitting Hepatitis B, C, or HIV through menstrual blood if the woman is a carrier."

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au

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