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The blood which renders a woman impure is uterine blood, which flows regularly during her menstrual cycle or irregularly in the case of a zava. In contrast, blood from a cut or tear in the vagina or uterus does not cause impurity. Additionally, uterine secretions do not cause impurity if they do not contain blood. Therefore, if the secretions are brown or yellow, they do not cause impurity; if they are red or black, they do. In cases of doubt, a rabbi or rebbetzin should be consulted. If the husband is asking, a rabbi should be consulted; if the wife is asking, any rebbetzin or woman who knows the halakha.
