In the Jewish tradition, the phrase "family purity laws" refers to laws governing sex within marriage. Contact with an impure person transmits impurity, and a person is impure when they have a discharge from their genitals. This impurity is eliminated by a dunk in a mikvah (a ritual bath), so a man, after a nocturnal emission, and a woman, after menstruation, must dunk before resuming "normal" sexual relations, and husband and wife should refrain from intercourse while a woman is menstruating. For an observant Jewish woman, this requires a monthly trip to the mikvah.