Thus, the investigators adopted an experimentally rigorous psychosocial paradigm in which sixteen undergraduate female participants were placed in a custom-built, computer-controlled “olfactometer” inside of which male faces appeared sequentially before them on a screen. One of five odors (two “unpleasant”: synthetic body odor, rubber; two “pleasant”: geranium, male cologne; and one “neutral”: clean air) was randomly pumped into the experimental chamber and paired with the face. There were forty faces in total, and each face was randomly presented three times so that every participant experienced it paired with at least one odor from each of the three categories (unpleasant, pleasant and neutral).
As you might expect, the young women in this study consistently rated the male faces as being significantly less attractive when presented with the unpleasant odors. In addition to these findings justifiably putting a smile on the faces of perfume company executives everywhere, there are other fascinating implications for such data, too. According to Demattè and her coauthors:
In the years to come, our findings might also be relevant in the technology sector, given recent developments in the area of multisensory applications, such as the possible use of olfactory cues in messaging applications, electronic picture storage/retrieval and enhancing the sense of presence in virtual reality.
I must say, I’m not entirely sure how that would look in practice (perhaps a spritz of sassafras from a designated pinhole in your iPhone to match your husband’s ring tone, or a scroll-down menu of scent accoutrements for Match.com profiles), but I do like the general idea.
As far as natural body odors go, scientists have found repeatedly that the less a person smells like you, the more attractive—or rather, the less repulsive—you find their armpit aromas. To evolutionary psychologist Glenn Weisfeld from Wayne State University, the reason we prefer dissimilarly scented others is obvious: since olfaction plays a key role in identifying who is genetically related to us and who isn’t (in some studies, participants with especially strong odor detection abilities can even successfully discriminate between the body odors of identical twins raised apart and those of fraternal twins raised together), being specially repelled by the malodorous fumes of our biological kin functions to promote incest avoidance.
To explore his basic evolutionary hypothesis, Weisfeld and his colleagues asked family members to smell each others’ body odors—not the most pleasant scenario, you’ll probably agree (for me an outright nightmare), but a necessary one for scientific purposes. A total of twenty-one families from the Ontario area participated in this study published in a 2003 issue of the Journal of Experimental Child Psychology. Each person in the family was given a new, all-white, identical t-shirt and was instructed to wear this shirt to bed for three consecutive nights. No scented soaps or perfumes were used during this odor absorption period, and shirts were kept in their own sealed plastic envelopes during the day.
After three nights, each family member was tested in isolation and asked to compare the shirt worn by another family member with that of an unrelated control subject (matched by gender and approximate age). The participants were asked first which odor they preferred, and then which shirt was that of their mother, father, child or sibling. A few interesting findings emerged from this study, some of which lends support to Weisfeld’s incest aversion hypothesis. First, both mothers and fathers could distinguish the smell of their own child but, somewhat curiously, mothers “strongly preferred” the odor of the control child. Fathers demonstrated a similar trend in odor preference, but for them the effect failed to reach statistical significance. Older children in the study (those aged 9-15 years) likewise preferred the body odor of the control adult man and woman to that of their parents. Furthermore, these older children strongly preferred the scent of control children in opposite-sex trials, but showed no preference for the body odors of their same-sex siblings versus controls. That is to say, brothers found their brothers’ body odors as mutually offensive as another boy’s body odor, and the sister pairs showed the same pattern of indifference response.
A final recent study worth mentioning was one conducted by Charles University of Prague anthropologists Jan Havlicek and Pavlina Lenochova, who actually answered the age-old question of whether carnivorous people smell worse to us than vegetarians. In other words, “the aim of this study was to test the effect of red meat consumption on axillary odor hedonicity.” In a 2006 article published in the journal Chemical Senses, Havlicek and Lenochova convinced seventeen disease-free, nonsmoking male students ranging in age from nineteen to thirty-one years to eat strictly defined diets. (They were paid about $35 for their participation in the study, a real bargain.) Half of the participants were assigned to the “meat” condition for two weeks, and the remaining half to the “non-meat” condition for this period.
During the first ten days, these males could choose from a list of prepared meals and had to select at least one main dish out of the list every day. “The individual dishes were elaborated,” write the authors, “to differ in meat content only (e.g., vegetable risotto/pork risotto).” The final three days of the special diet were even stricter; during this time, the participants were hand-served lunch and dinner to precisely control for their dietary intake—the meat group, for example, was observed wolfing down a 100-gram red meat dish for each main course. To rule out other possible factors, Havlicek and Lenochova forbade the participants from sleeping in the same bed as their partner, engaging in rigorous exercise, using perfume, deodorants, antiperspirants, aftershave and shower gels, eating garlic, onions, chili, pepper, vinegar, blue cheese, cabbage, radish, fermented milk products and marinated fish, consuming alcohol or other drugs—and even from having sex (those who confessed to such venal sins were excluded from the final data analyses). After two weeks on either the “meat” or “non-meat” diet, participants then switched to the other diet for the following two weeks, so that each man’s body odor was assessed on both diets.
At each two-week interval, thirty female students from the same university were asked to inhale the scent of cotton pads that had been affixed to the men’s underarms the entire day before. I don’t know whether it would have been worse being one of the male “odor donors” in this study and having to change my diet so drastically for such an extended length of time, or being a female odor judge and having my delicate olfactory sense pierced by even a moment of such miasmic horrors. (By the way, the women received a perfume tester and a chocolate bar for their help.) The ends justified the means, though, at least for the sake of vegetarian males in Prague. We now know that, even independent of where women are on their menstrual cycles, the “odor signatures” of men on a non-meat diet are perceived by fertile women to be less intense, more pleasant and more attractive than their meat-eating peers.
Now, if you’ll excuse me, I have the sudden urge to take a shower.
In this column presented by Scientific American Mind magazine, research psychologist Jesse Bering of Queen's University Belfast ponders some of the more obscure aspects of everyday human behavior. Ever wonder why yawning is contagious, why we point with our index fingers instead of our thumbs or whether being breastfed as an infant influences your sexual preferences as an adult? Get a closer look at the latest data as “Bering in Mind” tackles these and other quirky questions about human nature. Sign up for the RSS feed or friend Dr. Bering on Facebook and never miss an installment again.