Perfume and Pheromones: Why Beauty is in the Nose of the Beholder

Scents — whether natural or artificial — can influence what we find attractive and even how we see ourselves. J. Sibiga/Flickr

The saying goes that beauty is in the eye of the beholder. But attraction is based on more than love at first sight. We are also drawn to others by how they sound. And when we feel chemistry with another person, it may be thanks to one of our chemical senses: our sense of smell.

For many animals, the primary method of negotiating hook ups is by odor. When a female boar catches a whiff of a male’s musk, she finds it an instant aphrodisiac. But do humans also secrete pheromones? Or do those artificial pheromones — perfumes and colognes — have a similar effect on those we seek to woo?

Two new scientific papers reveal the links between odor and allure by examining how natural and unnatural scents influence what we think about the people we sniff.

Feminine fragrances

Around 80% of British women and 60% of British men use a deodorant every day. Almost all deodorants are perfumed, which means that most of us are masking (or perhaps exaggerating) our natural odor with a scent concocted in a laboratory. Deodorant manufacturers advertise their products to men as acting like super-powerful pheromones that are catnip to every passing hottie. Usually, adverts aimed at women focus on the femininity of the fragrance, by pointing to exotic floral ingredients like vanilla, rose, or jasmine.

The idea seems to be that perfumed antiperspirants make men smell more masculine and women smell more feminine. But is this true?

Caroline Allen, a PhD student at Scotland’s University of Stirling, had 20 men and women wear cotton pads under their armpits for 24 hours. These pads soaked up the volunteers’ sweat. The volunteers were asked to steer clear of foods that might influence their natural odor, such as garlic and curry. The normal procedure in body odor studies is to collect completely uncontaminated samples, so that the researchers have a good record of how their volunteers naturally smell. But in this experiment, Allen also had her volunteers collect sweat samples after applying their usual deodorant. Would sweat smell appreciably more masculine or feminine when mixed with scented antiperspirant?

The sweat samples were sealed in Ziploc bags and a very lucky (!) 130 people were recruited to huff each sample, rating for femininity and masculinity on a 7-point scale.

In women, the fragranced odors were rated 23% more feminine than the unfragranced odors. But there was no difference in how men and women rated the female odors.

For male odors it was a different story. There was no difference in ratings of masculinity between fragranced and unfragranced samples. Women did tend to rate fragranced samples as somewhat more masculine (15% more) than men did, suggesting that women are more sensitive to the change in body odor associated with male deodorants. But there were no overall differences in the masculinity ratings of fragranced and unfragranced samples.

Why might this be? One explanation could be that we culturally associate floral and fruity scents with femininity. When we inhale vanilla or jasmine we probably don’t confuse the smell with the natural body odor of a particularly feminine woman. Rather, we recognise that this is the kind of perfume a woman might choose if she preferred scents that our culture agrees signify femininity (and, conversely, that women who wish to avoid signaling their femininity may choose to shun).

Scents that signify masculinity may be less common. Men’s deodorants instead tend to be perfumed with neutral scents, like the smell of the ocean (for the man who wants to pong like a pirate in a storm). When women smell these scents, they may not be able to draw upon cultural associations between the odor and masculinity.

An alternative explanation is that deodorant manufacturers intentionally avoid hyper-masculine fragrances because men don’t want to smell too masculine. Although deodorant advertisements promise instant animal-magnetism after a single spray of deodorant, an excessively musky man may smell too macho. This is important because we know that straight women tend not to be attracted to very masculine men. There appears to be a sweet spot between an athletic physique and a man who is unattractively muscle-bound; an assertive personality that doesn’t tip over into arrogance. Perhaps a man who stinks like the rear end of a musk ox is thought to be so manly he’s unappealing.

So, it seems that deodorant companies are selling men on the idea of an appealing masculine odor, and then giving them an antiperspirant that — thankfully — doesn’t live up to the promise.

The Scent of Sex

So much for artificial pheromones. But what about the real deal? Do humans secrete natural odors that change the behavior of those who catch a whiff?

The general consensus among scientists is that, although body odor can affect attractiveness, humans don’t employ pheromones in the same way that other mammals or insects do. But recent evidence suggests that women do secrete a collection of chemicals that trigger various responses in men. These chemicals have been dubbed “copulins” because of their effects on sexual behavior.

In our primate cousins, various fatty acids are found in vaginal secretions. The fatty acids — the copulins — are more concentrated when females are most fertile. Female chimpanzees and stump-tailed macaques who produce more copulins receive more sexual advances from males.

Megan Williams and Amy Jacobson of Rutgers University in New Jersey decided to test for the effects of copulins on men’s mating psychology. Rather than collect real copulins, they whipped up a batch of synthetic copulin solution in the lab. The solution contained five fatty acids at concentrations identical to those shown by previous research to be associated with ovulation, the time in a woman’s cycle when she is most fertile. 5ml of the copulin solution was poured onto a gauze pad, which was then pinned onto the inside of a surgical mask.

One hundred straight men wore either a copulin-infused mask, or an untainted control mask, while completing a series of activities on a computer. They rated photographs of women’s faces for attractiveness, estimated their own sexual desirability, and answered questions on their mate-guarding behavior (how frequently they use various tactics to prevent their partner from pursuing other men, or to prevent men from pursuing their partner).

The results of the experiment showed that men in the copulin and control groups didn’t differ in their mate-retention behavior. Copulins apparently have no effect on jealousy, or at least self-reported behaviors inspired by jealousy. Ratings of women’s facial attractiveness were slightly higher in the copulin condition (14% higher), although analysis of this difference revealed that it was not statistically significant. We can’t be sure it’s a genuine difference.

However, copulins did have a significant effect on men’s estimates of their own sexual desirability. Men who sniffed copulins rated themselves 21% more desirable than men who sniffed fresh air.

It is unclear whether humans have evolved to use copulins in any meaningful way. Do women secrete copulins to attract the attention of men? Are men motivated by copulins to pursue women, or to compete with rival men? Another hypothesis mooted by Williams and Jacobson is that “copulins are a byproduct of our shared ancestry with non-human primates”. If true, humans may not be adapted to deploy or respond to copulins, but we do so (however slightly) because of a holdover from our tree-swinging ancestors.

So, do humans secrete and respond to pheromones? The answer seems to be yes, but our sexy secretions appear to be much less persuasive than those of our animal cousins.

Allen, C., Cobey, K. D., Havlíček, J., & Roberts, S. C. (in press). The impact of artificial fragrances on the assessment of mate quality cues in body odor. Evolution and Human Behavior. Read summary

Williams, M. N., & Jacobson, A. (2016). Effect of copulins on rating of female attractiveness, mate-guarding, and self-perceived sexual desirability. Evolutionary Psychology, 14(2). Read summary

For an audio version of this story, see the 3 May 2016 episode of The Psychology of Attractiveness Podcast.

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