Love Means Never Knowing Other Guys’ BO

Romantic love is so out of fashion these days—frowned on by feminists and bypassed by hookup culture—that I was surprised to find it the object of a scientific smell study.

Researchers Johan Lundström, at the Monell Chemical Senses Center, and Marilyn Jones-Gotman, at McGill University, looked at how romantic love alters a woman’s ability to identify male BO. Being psychologists, they start from a precise, if dispassionate, working definition of love:

heightened attention towards one’s partner, which in turn leads to heightened feelings of attachment, reward, and commitment.

Not much controversy there. The arguments start when scientists try to explain the biological and psychological mechanisms that produce this state. There are two contending hypotheses. Attention theory holds that romantic love is an increase in attention to one’s partner; deflection theory holds that the lover’s attention is deflected away from other potential partners. At the moment, neither theory has an overwhelming advantage: studies involving everything from oxytocin release to attraction ratings provide supporting evidence for both.

Lundström and Jones-Gotman took the novel step of testing attention and deflection theory using BO.

They recruited twenty young women who had been in a heterosexual relationship for the past 12 to 36 months. The lower limits rules out infatuations and the upper limit rules out the mature love that emerges in long-term relationships. (Yes, psychologists are all over the details . . .) The investigators measured how deep in love each volunteer was using Hatfield and Sprecher’s Passionate Love Scale. (Seriously. It consists of 30 statements such as “In the presence of my boyfriend, I yearn to touch and be touched.”)

Next, they collected BO from three groups of people: the young woman’s BF, her GF, and a non-romantic man friend. BO was collected with what First Nerve readers will recognize as a standard method: absorbent cotton pads sewn into the arms of T-shirts. The shirts were worn to sleep for seven nights, then placed in a deep freeze at -80˚ C.

Here’s the crucial part: each young woman had to identify her BF by sniffing three BO samples—one from him and two from other BFs randomly drawn from the freezer. Similarly, she had to pick her GF from among three GF samples, and her man friend from among three MF samples. 

As a group, the women could successfully identify their BF, their GF, and their MF by smell. They did so equally well across the groups.

However, a woman’s ability to identify her man friend’s BO varied negatively with her score on the Passionate Love Scale. In other words, the more in love she was, the less able she was to correctly pick out her MF’s BO from those of other men—just as deflection theory predicts.

Degree of Passionate Love had no effect on a woman’s ability to identify her BF’s BO—again as predicted by deflection theory. (Attention theory predicts that BF detection should increase with Passionate Love.) And finally, the effect was sexual preference-specific: Passionate Love did not alter the ability to identify same-sex friends by BO. 

The more in love with their boyfriend participants reported themselves to be, the worse they performed in identifying the body odor originating from an opposite-sex friend—a potential partner for these heterosexual women.

The results are a clear win for deflection theory. It appears that love dulls the wandering nostril.

The results also drive home a point I make in What the Nose Knows—smell is about the brain as much as it is about the nose. Cognition and emotion alter the way the brain filters raw odor perception from the nose. In this case, romantic love retunes our smell abilities in a remarkably subtle way.