Why is a woman’s menstruation considered unclean?


“If a man has sexual relations with a woman during her monthly period, he has exposed the source of her flow, and she has also uncovered it. Both of them are to be cut off from their people.” Leviticus 20:18
            Touching blood whether from an animal or a wounded person always made the person unclean for a period of time, sending them to quarantine for seven days outside the camp.  Blood carried diseases in it and God wanted his people to stay healthy.
            Menstruation is bleeding and the woman needed to touch her own blood.  According to the rules, she required separation.  If she had sex with her husband during her “flow,” he too needed to be removed from the people for seven days.