The enduring riddle of ‘menstrual synchrony’: an anthropological perspective


The discussion on female menstrual cycle synchronization may be as old as the recorded history of sexuality, and raises important questions about gender relations, notably the ‘female group solidarity effects’ that may possibly be constructed by it, or through it. Remarkably, already an ancient Egyptian text from the 12th century BC, on the ostracon OLM 13512, has registered the ritual isolation of women for their menstrual periods, and hints at their possible synchronization. Terry Wilfong’s comparative analysis of this piece of text from Deir el Medina has suggested that menstrual synchrony was assumed to occur among the local women. Synchronization might likely be a response to a male-enforced taboo on menstruating women to freely mingle with others that existed in this Egyptian and many other cultures, a practice that allowed women’s identification and marking vis-à-vis men.

Synchronization of menstrual cycles has been reported in many societies, and the phenomenon features prominently in world folklore as well as a number of non-literate cultural traditions (Yurok, Hadza, Australian aboriginals, !Kung, or Bedouin), often in connection with the moon cycle. It has now also ‘urban myth’ aspects in Western society, with many girls repeating after each other that ‘it just happens’. But the historical origins and development of menstrual synchrony are rather unknown and hardly explored and references to it are rare (Although it was suggested by anthropologist Chris Knight back in 1987, in a sweeping theory of culture, that menstrual synchronization by women was a strategy towards men to urge them to hunt and secure the products of the hunt: a kind of archetypical cultural situation). The most that can be done, however, is describing and testing alleged empirical examples and see how they ‘function’ in a given society. Existing descriptions are all of rather recent date.

The scientific discussion on menstrual synchrony is only some four decades old. It is a fascinating and dynamic debate that has gone through the evidence from many sides. Menstrual synchrony can simply be defined as the gradual aligning of (the onset of) menstrual cycle timing and length among adolescent girls or women living in close proximity and frequently interacting. The scientific case was first made by psychologist Martha McClintock on the pages of the famous journal Nature in 1971, based on the study of a group of US college dorm girls, living in a closed setting of a certain intimacy, whereby physical factors might have stimulated the unconscious synchronization of their periods. Since its appearance, the paper’s data and interpretation - hinting also at the existence of human pheromones (chemical scent-like transmitters emitted from one human to another that could impact on the psycho-biological functioning of others) – have been controversial. The study led to both corroboration and refutation in subsequent field research, predominantly done among respondents from Western societies. In the last few years, sceptics seem to gain the upper hand in a sustained offensive against the whole idea. But the case is still not closed.

There may be a ‘paradigmatic’ controversy at stake here, where both opponents and proponents stick to their epistemological positions and do not or cannot cross the line. I did a study (*) in a non-Western field setting – among the Suri people, a small, non-literate agro-pastoral community in southwest Ethiopia – and based on longitudinal research, which suggests that neither a purely physiological and quantitative approach nor a merely interpretive one is sufficient to provide the answer whether menstrual synchrony ’exists’. My paper suggests that both opponents and proponents have phrased the question wrongly. It argues that menstrual synchrony is not a straightforward psycho-physiological process that always occurs under comparable circumstances of female proximity and ‘pheromone exchange’ and therefore ‘is a fact’. Neither is there an invariant evolutionary sequence or pattern in menstruation that would exclude the occurrence of menstrual synchronization, as some of the sceptics suggest. The research among the Suri of Ethiopia confirmed that ‘menstrual synchrony’ seems to occur but is indeed precarious. It is in part a social-cultural phenomenon, but one that tunes in to psycho-physiological processes and produces real behavioral changes in bodily timing of menstrual occurrence. Of course, we know from the historical record that in extreme cases, such as women in concentration camps, menstruation can just stop, due not only to sustained malnutrition but also because of deep distress and lack of the will to live among the women. In normal conditions, menstrual synchrony is neither independent of societal conditions and cultural engineering, and can be ‘produced’. In addition, the role and workings of pheromones in the process seems increasingly doubtful. As Little et al. already noted in 1989, environmental influences (may) cause menstrual synchrony, not pheromones. In all, it seems that specific social and historical conditions relating to the creation of ‘female spaces’ influence its emergence and development. But it is often difficult if not impossible to sketch how those female spaces themselves emerged over time, especially in non-literate cultures such as Suri.

In the field research on the Suri people, a rather self-contained Ethiopian ethnic group with little intermarriage with neighboring peoples, two groups of young, unmarried females – who spend all of their days (and most nights) together in close-knit groups and come into intimate physical (but not homo-erotic) contact - were followed and interviewed/observed over a period of 6-7 months, with a follow-up study of partly the same women in the same setting 10 years later. Suri sexual culture values female independence and personal choice. Adolescent girls and women are the decision-makers, initiating sexual liaisons and marriages, and no union is concluded without their consent (in contrast to that of neighboring ethnic groups). There are no religious factors inhibiting this. Young women have and value premarital sex, but culturally are not allowed to get pregnant before wedlock. They usually succeed in preventing it, planning well and practicing well-timed sexual abstinence mainly via the rhythm method. Also the moment to first get pregnant after marriage is carefully planned. This management of sex and pregnancy is based on intimate, correct knowledge of the menstrual cycle and the facts of human reproduction, not transmitted in school settings but from mother to daughter. This knowledge is also rehearsed and practiced in the solidary girls’ groups that they are part of when they are ca. 14 to 22 years old. These groups are both work units and leisure-time units. For instance, the girls go out simultaneously to look for sexual liaisons on certain nights of the month. Marriage is concluded relatively late for Suri girls: only when they are in their early twenties. All this suggests that Suri women are self-conscious about their sexual identity and their central future role as mothers/wives, which they combine in a behavioral pattern that fuses the enjoyment of sex with a show of this reproductive power or capacity vis-à-vis future husbands. The village study found that when young newcomers entered the girls’ groups (two different groups of 19 and 10 girls were studied) they had different dates for the onset of the menses. But after 6 to 7 months they all had brought the stating date more in line with the average of the group. Although no strict concordance was seen, synchronization definitely occurred, with dates of menstruation onset among the novices delayed and cycles sometimes one or two days longer or shorter than before. Perhaps this was because it was ‘convenient’, fitting the rhythm of sexual life and other activities of the group as a whole. Girls always said: “We align our period of blood with the moon (cycle)”. They ‘wanted’ to have the same timing of menstruation, otherwise they would, for example, miss out on the activities of the rest (the older girls) of the group and miss valuable experience. It appears that the menstrual pattern adaptation was due to group pressure in line with socio-cultural preferences, hence an ‘artifact’, but real and accomplished in interaction with physiology). Here an adaptive effect may be visible, but a culturally styled one. Pheromone influence, however, was unlikely (although there is research suggesting the contrary): all seemed to be set in motion by group pressure and the girls’ wish to be part of things and in control of sexual activity at the right time (As humans lack a functioning ´vomeronasal´ organ - in contrast to many other mammal species - to detect them, there is still great uncertainly on the relevance of pheromones. The olfactory system may play a role, however, although not in a determinate sense). After marriage, the need to synchronize menstruation wanes for the Suri women because of domestic life activities and the wish to bear children. But married women also carefully plan their pregnancies, an issue on which husbands have little to say. Women even plan the specific day (or night) for intercourse or conception - by non-verbal symbolic communication to the husband. They also consciously space births (with at least 2,5-3 year intervals) in order not to be overburdened with child care in a busy life.

In Suri female sexual culture we thus see a specific interaction of socio-cultural preferences – expressing women’s control over sexual and reproductive issues – and bodily and physiological facts, among which is a certain variability or adaptability of the menstrual cycle (and focused, purposive interaction with males). This empirical case study thus showed the conscious mutual influencing of biological and socio-cultural factors, evolved over time, and may allow us to go beyond a dichotomous view of menstrual synchrony either ‘existing’ or ‘not existing’. A better, context-sensitive combination of quantitative, physiological methods and qualitative research (via in situ interviews and observations in natural settings) can clarify how these interactions work. As suggested above, a more or less conscious female strategy for of differentiation and claims to autonomy towards men is involved. This notion was also suggested in a very recent paper, published as the field study on the Suri girls, described here, was in press. But we do not know when this specific ‘female space’ among unmarried Suri girls emerged and how their preference for menstrual synchrony was historically developed. Neither are there specific initiation ceremonies for Suri women that emphasize sexual or gender identity or reproductive values. Again, we could say that ‘more research is needed’, but the fact remains that tracing the historical origins will be a big challenge. The only clear conclusion is that Suri young women at some point developed this system of synchronization for various sexual and social purposes and were able to enhance their position vis-à-vis men. It testifies to their remarkable cultural inventiveness.

(*) See: J. Abbink, 'Menstrual synchrony claims among Suri girls (Southwest Ethiopia): between culture and biology. Cahiers d’Études Africaines LV(2), no. 218, pp. 279-302 (Available on: www.


Jon Abbink works as a research anthropologist at the African Studies Centre, Leiden, The Netherlands (

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Comment by Jon Abbink on August 29, 2015 at 10:23am

Typo: I mean "this is an unconscious effect" (line 7)

Comment by Jon Abbink on August 29, 2015 at 10:20am

Hi Sydney,

Many thanks for the comments!

I must say I am not sure about the first point. I do not think that Suri girls are aware as such of ovulation. I did not specifically look into it; I went by the coordinated efforts I saw among them to synchronize in order to be able to have 'safe sex' on selected nights. In the paper I say that the Suri girls expect, or desire to have reached, a concordance in ovulation with the others in the context on synchronization, but they is an unconscious effect, I think. They did not verbalize this to me.

On the second point: no, the Suri women do not have a idea of association or causal connection between moon and fertility; they associate the cycles of the moon and females. They are virtually the same. In the paper I mentioned an interesting reference to this.

Comment by Sydney Yeager on August 26, 2015 at 7:15am

Jon, this is a interesting ethnographic discussion, thank you for sharing this. You may mention this in your article, I haven't had the opportunity to read it yet, but how aware do you think the Suri females are of their ovulation?  In the West there are of course lots of scientific tools to help women attempt to calculate ovulation. Yet I doubt many women feel like they have the degree of physiological agency over their reproductity you describe.  I am aware of anecdotal that evidence suggests that some women can feel ovulation, I'd describe it as a twinge on one side ranging from a flutter to a stitch in the side sensation that is brief less than 30 seconds. I've always wondered if this isn't a milder healthy form of the same phenomenon which in painful pathology is diagnosed as Mittelschmez. This and other subtle signs are available to women if they are trained to interpret them. Do Suri females share knowledge for interrupting these signs?  I mention this because of the importance you place on women's agency over their sexuality and reproductivity. Perhaps menstrual synchronization is a side effect group solidarity and physiological agency which has more to do with observing and controlling ovulation.  I'm also interested in how they conceptualize their menstruation and fertility. You mentioned the moon. As I type this question, I realized that the idea of "it" being a cycle is part of my own conceptualization. Do they have belief about the moon and fertility or is it just the connection of the cyclical nature?

Comment by Jon Abbink on August 22, 2015 at 1:13pm

Thanks; I included the reference now.


Comment by Huon Wardle on August 21, 2015 at 5:15pm

A very interesting report, thanks. Where are you publishing the field study?


OAC Press



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