At some point in history, Jewish women used to have very regularly scheduled Monthly cycles, and used to have some sensation that accompanied the onset of menstruation. Both of these play important roles in Halacha. The monthly cycle establishes what is called a וסת קבוע, which affects what days a woman has to take into account that her menstruation is about to begin. The sensation (הרגשה) is a Biblical prerequisite the absence of which prevents blood from creating ritual impurity, according to most opinions.

At some point in history, women stopped having both of these. The earliest discussion of the cessation of הרגשה that I have seen is in the שב יעקב, circa 1750. The Aruch HaShulchan (early 20th century) asserts that women still have הרגשה, they just don't know what it is well enough to recognize it, but this is just a different way in which it was lost (it became undetected).

Rav Yaakov Kaminetzky reported that when he was in Europe most women had regular Monthly cycles. Today, it is very rare, although apparently not unheard of, from what I have been told.

My question is - is there any Rabbinic speculation about why these changes, with significant Halachic ramifications and/or implications, occured when they did? Are they associated with any world events? Is there any metaphysical significance attributed to the changes?

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    Why do you assume that nature has changed? Most women have pretty regular periods and lots of women have hargasha. If you count the feeling of blood flowing then pretty much all women have hargasha. Commented Sep 21, 2014 at 17:34
  • @RobertS.Barnes ask almost anyone who gets niddah shailos and they will tell you that almost no one has an exact 30 day down to the daytime/nighttime cycle (or any perfectly consistent interval). Many women vacillate around a certain range, but the exact precision required for halachic kevios vesset is virtually nonexistent. "Blood flowing" is not enough - it has to specifically be the feeling of blood flowing out of the womb - see pischei teshuva to Y.D. 183. These "facts" aren't my inventions - they are noted by halachic authorities. Commented Sep 21, 2014 at 18:54
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    @YEZ As you know the Noda' Bihuda disagreed with that Pitchei Teshuva
    – Double AA
    Commented Sep 21, 2014 at 19:03
  • The Aruch Hashulchan, when discussing this issue, does not contend that hargasha is a simple and obvious thing that all women feel - he acknowledges that none of them experience what a hargasha is, but they must just not be sensitive enough or not paying enough attention. Commented Sep 21, 2014 at 19:06
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    @RobertS.Barnes Re-read my question. I explained why. Poskim talk about it. Overtly. Explicitly. Directly. They discuss what to do with the change. I am not innovating anything here. I am repeating what they say and asking for an explanation. Why is this so troublesome? The Shev Yaakov explicitly says it. The Aruch HaShulchan discusses it. R' Yaakov Kaminetzky explicitly said that it specifically changed during his Rabbinical career. What more evidence do you want me to bring? I can't travel through time to bring you a woman to ask her. Commented Sep 21, 2014 at 19:11

5 Answers 5


This was raised in Europe already - see Taharas Yisrael I think. Note that the painful menstruation which woke women from sleep was much more common.

With higher percentages of body fat, they have more hormones perhaps.

Joking aside -

Perhaps steady low calorie diet when young puts the girl into Strong Pattern. Some women from poor countries such as Thailand kept their patterns even in USA.

This is based on small sample size.

Hormones in food - if ingested in quantity - can affect a cycle.


Here is a partial answer to your two part question. I have heard from the Rabbis I learnt shmattas with in the name of Rav Bic & Rav Menasheh Klein who both independently attributed the erratic vestos to the suddenly widespread use of electric lines.

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    Im afraid i dont see how electric wires would do that
    – Double AA
    Commented Sep 19, 2014 at 3:51
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    "shmattas"? Is that (in this case) Yiddish for (the checking of) edim?
    – msh210
    Commented Sep 21, 2014 at 5:18
  • @msh219 yes. Thats exactly what it means.
    – user6591
    Commented Sep 21, 2014 at 5:32
  • @Double AA These ideas were said in the 70s at the height of connecting cancer to electric magnetic feild from transformers and power lines. Nowadays studies are less conclusive in that respect, but the assumption is that the human body which is definitely affected by these phenomena to some degree when subjected to a given large amount, were at least affected to a lesser degree from smaller amounts.
    – user6591
    Commented Sep 21, 2014 at 5:38
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    @YEZ I disagree! Rabbis can speculate that science is at play here.
    – Double AA
    Commented Sep 21, 2014 at 19:10

Could it be the electric lights that affects the cycle?

This scientific paper discusses how lighting affects ovulation. Ovulation in turn usually precedes menstruation by a fixed number of days even in today's day and age.

This may explain why some women used to have their cycles linked to the day of the Jewish month; i.e. the cycle of the moon. Moonlight matters a lot more when you didn't have electric lighting.


There is little rabbinic speculation in an halachic context for why this changed but the standard explanation is that modern lighting and and nutrition have caused this change.

I know who had difficulties with cycles causing her to be a nidda too frequently. She was advised to use dimmer lights at night and no light at all when she slept and it worked.

I was also by a nurse who had volunteered for Doctors without Borders that in third world countries women's menstrual cycles and experiences are the same as they were in ancient times.

  • Artificial lighting is what I've heard as well; it keeps us off from our natural rhythms. It's said when Yemenite Jews moved from a non-electrified civilization to yes-electrified Israel, they noted this phenomenon -- from kavua to not.
    – Shalom
    Commented Oct 18, 2021 at 22:59

I am a Rabbi I speculate that the cycal is not set anymore

maybe becouse of feminism, since the woman stopped staying at home, or at the shtetal (some woman still have a set one) so through Menstrual synchrony (by meeting a lot of different woman that have different cycles daily) the set cycle got ruined see first comment above of @user6591


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