Is the Menstrual Cycle Linked to the Timing of Sexual Assaults?

Is ovulation a dangerous time for sexual assaults?

Posted Jul 28, 2011


The menstrual cycle has a profound effect on women's behaviors, preferences, and desires. In a book chapter that I recently published with Kristina M. Durante (see chapter 7), we explored how the menstrual cycle might manifest itself in various organizational settings. We hypothesized that sexual harassment within the workplace might differentially occur as a function of women's menstrual status. Although we did not empirically test our hypothesis, to our knowledge this constituted a rare attempt to link criminal acts committed against women to their menstrual cycles.

I recently came across a paper that tested our general hypothesis albeit in a non-organizational setting and for a crime that is more heinous than sexual harassment. In a forthcoming paper in the Journal of Forensic and Legal Medicine, Patricia Beirne, Janet Hall, Claire Grills, and Tara Moore sought to establish whether sexual assaults on women in Northern Ireland covering the years 2002-2009 were more likely to occur during a woman's fertile phase of her menstrual cycle. The theoretical predictions are not straightforward to make. On the one hand, several studies have found that women tend to engage in greater sexual signaling (e.g., dress more provocatively) when in the fertile phase of their menstrual cycle (Durante, Li, & Haselton, 2008; Grammer, Renninger, & Fischer, 2004; Haselton et al., 2007; Saad & Stenstrom, 2011). If so, this might place them at greater physical risk. On the other hand, conflicting research has uncovered that when maximally fertile, women engage in lesser risk-taking (e.g., walking down a dark alley; Bröder & Hohmann, 2003; Chavanne & Gallup, 1998). As such, it is unclear whether the net effect would yield a differential rate of sexual assaults during the fertile phase.

Returning to Beirne et al., they did not find a statistically significant correlation between a given day within the cycle and the number of attacks on that day. However, when the data was parsed in different ways, a clear pattern did emerge. For example, when the cycle days were split into three menstrual phases, the fertile phase (mid-cycle) contained one-third more attacks: early cycle = 33 attacks; mid-cycle = 42 attacks; late cycle = 30 attacks). Perhaps more telling, 19.6% of all attacks occurred within the three-day window of maximal fertility (days 14 through 16). This is quite an extraordinary finding as it clearly highlights that the probability of an attack is not equal across all days of the menstrual cycle.

Of note, this finding does not resolve the all-important question of establishing the causal forces behind this temporal effect. Is this phenomenon largely driven by the differential behaviors of women across their menstrual cycles and/or is it mainly due to perpetrators' ability to accurately gauge the fertile status of women?

Lest some readers might be led astray by their anti-evolutionary psychology logic, exploring a possible link between the menstrual cycle and sexual assaults in no way condones or justifies any violence committed against women. Furthermore, such a link does not in any way shift the blame to the victims. I mention this here because I recently received an email from a woman who was going through my recently released trade book, The Consuming Instinct: What Juicy Burgers, Ferraris, Pornography, and Gift Giving Reveal About Human Nature. Here is her original email to me:

"I couldn't find anything in the index of your book, Consuming Instinct, to point to data supporting your claim (plates, p. 4) that women dress more provocatively during the fertile phase of their menses in order to signal sexual receptivity.

I can only speak for myself, but I would be interested to know how many women you spoke to who claimed to do so themselves.

Perhaps you have not noticed that this is a highly problematic contention, not least as it is still used as a defense for rapists."

My reply:

"See notes 58 and 59 for the relevant references on p. 309. The Saad & Stenstrom paper is now forthcoming in the Journal of Consumer Psychology.

The scientific finding exists independently of how it might be misused by cretins and criminals. Surely, you are not suggesting that scientific results should not be reported lest they might be misused for all sorts of sinister reasons. If this were the case then little scientific work would ever be published (or only research that you approve of).

Thank you for your email."

Her rebuttal:

"Not at all suggesting that research should not be published; only commenting that on skimming the book, while receiving it into an academic library collection, neither the provocative pairing of illustrations nor the index pointed me to any support for the provocative contention.

Thanks so much for the clarification."

Apparently, this woman did not find it necessary to verify the references in my book to determine whether I had provided relevant citations in support of the "provocative" claim.  Also, note the number of times that she used the word "provocative" in her emails. Hence, at first she proclaims that this research is apparently dangerous, as accused rapists might use it as a defense strategy. Subsequent to my rebuttal, she still maintains that this is a very provocative contention. It is worth noting that all four authors on the Beirne et al. paper discussed in this post are women, as are many of the menstrual cycle researchers listed in the references below (Martie Haselton, Kristina Durante, Tara J. Chavanne, Natalia Hohmann, LeeAnn Renninger, Bettina Fischer, Mina Mortezaie, Eizabeth G. Pillsworth, and April Bleske-Rechek). I wonder if the woman in question thinks that these female scientists are all colluding in their quest to "promote a defense strategy for rapists." Nice.


Bröder, A., & Hohmann, N. (2003). Variations in risk taking behavior over the menstrual cycle: An improved replication. Evolution and Human Behavior, 24, 391-398.

Chavanne, T. J., & Gallup, G. G., Jr. (1998). Variation in risk taking behavior among female college students as a function of the menstrual cycle. Evolution and Human Behavior, 19, 27-32.

Durante, K. M., Li, N. P., & Haselton, M. G. (2008). Changes in women's choice of dress across the ovulatory cycle: Naturalistic and laboratory task-based evidence. Personality and Social Psychology Bulletin, 34, 1451-1460.

Grammer, K., Renninger, L. A., & Fischer, B. (2004). Disco clothing, female sexual motivation, and relationship status: Is she dressed to impress? Journal of Sex Research, 41, 66-74.

Haselton, M. G., Mortezaie, M., Pillsworth, E. G., Bleske-Rechek, A., & Frederick, D. A. (2007). Ovulatory shifts in human female ornamentation: Near ovulation, women dress to impress. Hormones and Behavior, 51, 40-45.

Saad, G., & Stenstrom, E. (2011). Calories, beauty, and ovulation: The effects of the menstrual cycle on food and appearance-related consumption. Journal of Consumer Psychology (conditionally accepted).

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