"[I]t's hard to find a society, a religion or a part of the world that does not find some way to make women feel dirty, guilty, unworthy or dangerous because of their monthly cycle. "Menstrual taboos are so widespread, they're almost a cultural universal," says Beverly Strassmann, evolutionary anthropologist and biologist at the University of Michigan who studies menstrual taboos. Yet there are exceptions: societies that treat menstruating women with respect. The negative associations with menstruation are well-known. Women may be prohibited from sexual intercourse, banned from places of worship or segregated in special huts. Various theories about the widespread prohibitions and restrictions range from false beliefs that menstrual blood carries toxic bacteria to fears that the blood triggers castration anxiety in men to beliefs that the smell of the blood disturbs animals and interferes with hunting."