2,057. When a Woman is Rendered Unclean

Hilchos Issurei Biah 5:1

Whether we’re discussion niddah (menstruation) or zivah (another type of flow), a woman is rendered ritually unclean by circumstances beyond her control. For example, if a woman jumped from one place to another, saw wild or domesticated animals or birds mating, or was stimulated and started bleeding. In these and other such cases, since she bled, she is rendered ritually unclean. A woman is rendered unclean by the smallest amount of blood, even a drop the size of a mustard seed.

Hilchos Issurei Biah 5:2

Women are rendered ritually unclean when blood is found in the outer chamber of the genitals. Even if blood did not flow outside the body, but rather flowed from the womb and no further, since it came from the upper part of the vaginal canal, she is rendered unclean. This is so even though the blood is still inside her body as per Leviticus 15:19, “within her flesh, a discharge of blood.” The upper part of the vaginal canal reaches to the place where the man’s organ reaches when completely inserted during intimacy; the upper part of the vaginal canal is like the uterus.