ויקרא, פרק ט״ו, פסוק כ״ד

Intimate relations with a menstruating woman result in a severe state of impurity. This is the only instance where a complete seven-day period of impurity transfers to another person, a direct consequence of the highly intimate contact with the source of the impurity [The Torah]. Because the focus here is strictly on the mechanics of purity and impurity, the situation generally assumes an accidental encounter. An intentional act of this nature carries the severe penalty of being spiritually cut off [אבן עזרא, רד צ הופמן].

The law applies to actual intercourse of any kind, not merely sharing a bed, and takes effect even without a seminal emission [רלב״ג, רד צ הופמן, תורה תמימה]. Regarding the man involved, commentators differ on who is included. One approach suggests the language excludes young minors, though it includes a child of nine years and one day who is physically capable of the act [תורה תמימה, אדרת אליהו]. Another perspective argues that the phrasing establishes a broad rule that does not exclude anyone [מלבי״ם]. Furthermore, this specific transfer of impurity applies only to a menstruating woman, not to a woman afflicted with the Biblical skin disease [חזקוני, תורה תמימה].

A person might mistakenly assume that the man simply adopts the woman's existing schedule. For example, if the act occurred on her fifth day of impurity, he might expect to be impure for only her two remaining days. To prevent this misunderstanding, the law clarifies that he begins his own independent seven-day count from the moment of the act, regardless of whether the woman purifies herself that very evening [רש״י, בכור שור, מזרחי]. The concept of her impurity passing to him means they share the same legal status, not the same timeframe. The man becomes a primary source of impurity, just like the woman, meaning he can transfer impurity to other people and to earthenware vessels [רש״י, רש ר הירש, ברכת אשר].

This shared legal status also yields two unique rulings. First, a betrothal with a menstruating woman is completely valid, unlike betrothals involving other severe prohibitions, because her forbidden status is only temporary. Second, if a couple is engaged in permitted relations and the woman suddenly discovers she has become impure, the husband must not withdraw abruptly. He is required to remain close to her until his physical arousal naturally subsides [תורה תמימה].

Despite sharing a similar status, there is a sharp contrast between the man and the woman regarding the items they lie upon. While a menstruating woman transfers a severe degree of impurity to her bed, the man transfers only a light impurity to his. His bed does not have the power to make people or clothing impure. Instead, it becomes a lower-level source of impurity that can only affect food and drink. The sages describe this dynamic by noting that the bedding beneath this man carries the same minor impurity as the blanket resting on top of a man with an unnatural bodily discharge [רשב״ם, רש ר הירש, רד צ הופמן].