Men Probably Can't Actually Smell When Women Are Most Fertile

Popular culture is full of scientific myths. No, the average person does not only use ten percent of their brain; sugar doesn’t make kids hyperactive ; and your hair and fingernails don’t continue growing after you die. But there’s one in particular which, on the face of it, seems to have at least some scientific basis: the idea that men can tell when women are ovulating by their scent.

It’s an idea that seems to pop up every decade or so. Here’s a study from 2020 that supports it, for example; here’s one from 2009 saying the same. Another study, this time from 2004 , reiterates the idea; here’s one from 2001 suggesting it’s true; you can even go all the way back to 1975 and find papers still saying the same thing. Men, it seems, can smell fertility in women.

But just how accurate is this factoid? According to the results of a new study, potentially not very: “Using frequent odor samples from the same women and hormonal assessment of fertility, we assessed potential fertility-related shifts in axillary body odor in a twofold study combining perceptual and chemical evidence,” write the authors. “Overall, there was no compelling evidence that female fertility positively affects male odor ratings.”

In fact, not only can men probably not pick up on the changes in a woman’s scent throughout her menstrual cycle, but those changes may not even exist at all : “The chemical composition of a woman’s axillary odor was not affected by her current fertile state,” the team discovered, or her "fluctuating ovarian hormone level.”

All of this adds up to the question: where did this notion ever come from?

Well, one clue may be in the methodology of this study versus previous research. “In most studies, men assessed fertility information of one woman over her cycle, thus simulating repeated encounters with the same woman,” the authors explain. In contrast, the new study “aimed to investigate whether men are able to detect female fertility from a single encounter.”

To that end, the male participants in the study were given 24 odor samples to rate over two separate sessions. No man received a sample from the same woman twice; the samples were distributed completely randomly, and rotated around the room systematically until every man had sniffed every woman.

And the results, if anything, showed precisely the opposite of what you’d expect. “In contrast to our predictions, axillary odor was descriptively evaluated as both less attractive and less pleasant at higher conception risk,” the authors noted – though the effect was very weak. Overall, they concluded, “we found no compelling indication that men’s perception of female axillary odors varies with female fertility.”

But another reason for the discrepancy between previous studies and the new paper is even more basic. “The majority of [prior] evidence lacks a direct assessment of female reproductive hormones, reliable hormonal confirmation of ovulation and depicts considerable inconsistencies in estimating the fertile window,” the authors point out – or to put it another way: nobody actually checked if the women really were ovulating when they thought they were.

This paper, on the other hand, confirmed where in their fertility cycle female participants were via both urinary and saliva samples. Not only that, but the team utilized cutting-edge technology to objectively evaluate the women’s aromas: “Chemical profiles of women’s axillary odor, measured with gas chromatography–mass spectrometry […] were used to assess whether changes in the abundance of chemical compounds occur in association with female fertility,” they explain.

Combine all this with the well-documented publication bias against null effects – that is to say, people aren’t that interested in reading studies that don’t tell them weird things like “men can smell when you’re ovulating” – and it basically adds up to a never-ending circle of confirmation bias.

So, it may be true that men can subconsciously tell when a woman is ovulating – but not an unfamiliar woman, and not by her scent alone. All in all, the most we can conclude is “more research needed” – including, as the team points out, revisiting some of the old results that got us here in the first place.

“We are certainly still at the beginning of understanding the physiological interaction between the gradual fluctuations in fertility and ovarian hormones across the ovulatory cycle and women’s body odor,” the paper concludes. “We strongly encourage further disentangling the physiological basis as well as the social function of olfactory cues to female fertility in humans with the robust methods we have at hand.”

The study is published in the Proceedings of the Royal Society B: Biological Sciences .