A woman becomes a niddah when she experiences uterine bleeding accompanied by a "hargashah."

(I use the word "niddah" the way we use it in everyday speech, to refer to uterine blood as dam niddah. Today, whether a woman experiences niddah bleeding or zivah bleeding, the practical halachah is identical: she performs a hefsek taharah and counts seven clean days before immersing in a kosher mikveh.)

Now let us define hargashah. Again we begin with the verses:

"And if a woman has a discharge, and her discharge in her flesh is blood, she shall be in her state of niddah for seven days." (ויקרא טו, יט)

Shmuel teaches in the Gemara that the word "in her flesh" (בִּבְשָׂרָהּ) establishes that a woman becomes a niddah by Torah law only if she had a hargashah — a bodily sensation — immediately before the blood emerged.

Three kinds of hargashah

The poskim offer three explanations of which sensation counts as a hargashah:

1. Opening of the cervix

A sensation of the uterus opening before the blood is released.

2. A tremor through the body

A sensation of trembling or shuddering.

3. A flow of liquid

A sensation of fluid flowing.

The third sensation — the only one still common

The first two are almost unheard of today. The third, a flow of liquid, is reported fairly often.

Poskim differ on how to treat it:

The reality today — most women feel nothing

The fact we have to deal with is that the great majority of women today experience none of these sensations immediately before menstruation. (If they do not occur immediately before the bleeding, they are not a hargashah.)

Three main approaches address this:

The three contemporary approaches

1. Rav Shlomo Levi

Women today do not notice the hargashah, but it is occurring. So even when a woman says she had no hargashah, we assume she did — even if all she saw was a stain.

2. The Tzitz Eliezer

Women do notice sensations, but the vocabulary we have for bodily sensations does not match the vocabulary of the poskim. So when a woman is menstruating, the sensations accompanying her period count as a hargashah. If she experienced only staining, we do not assume there was certainly a hargashah.

3. Rav Warhaftig

Women today do not experience hargashot at all. So unless a woman insists that she had one, we assume she did not.

Why does it matter? Isn't she a niddah either way?

Yes. A woman who experiences bleeding is a niddah in every respect, even if she is certain she felt nothing. Hargashah still has two main practical applications.

First — stains

With ketamim (staining), determining whether the woman experienced a hargashah is decisive. It can, though it does not always, make the difference between a ruling of taharah and one of tum'ah. We will take up the practical assessment of stains shortly.

Second — the obligation to do a bedikah

It is worth knowing all three sensations (opening of the cervix, a tremor through the body, a flow of liquid), because a woman who experiences the specific sensation of the cervix opening, or of a tremor through the body, is required to perform an internal bedikah.

Chazal understood a hargashah to signal that something has been released from the uterus. If there was a hargashah, we assume some discharge was released, and the woman now needs to establish whether that discharge contains blood.

Since the third sensation, a flow of liquid, is a machloket among the poskim, a woman who thinks she experienced it should ask a rav or a yoetzet whether a bedikah is in fact required before she performs one.

Practical halachah

It's worth noting any distinct bodily sensation she experiences immediately before bleeding or during her period. That information can matter when she finds a stain and needs to ask a halachic authority whether the stain renders her a niddah. A woman who notices no particular sensation has nothing to worry about.

A woman who feels the sensation of:

is required to perform an internal bedikah.

If she feels a flow of liquid, she should ask whether a bedikah is required. As noted, most poskim count a flow of liquid only when the sensation is internal. An external sensation of moisture or fluid is not a hargashah.