Sick of How You Smell?

Scientists show that differences in our vulnerability to disease affect how much we prefer our own body odor and the body odor of others.

Dr. Robert Burriss
Apr 7, 2016 · 5 min read
Our natural perfume can attract, or repel, potential mates: and sometimes ourselves! WackyStuff/Flickr

Our vulnerability to illness affects how we perceive our own body odor and the body odor of others, say scientists from the University of Warwick (UK). Variable body odor preferences may be an evolved mechanism that slows the spread of disease.

Body odor, attraction, and disease may not seem like natural bedfellows. But finding a mate and resisting infection are two of the most important challenges faced by any organism, and humans are no exception. If we succumb to a disease, we won’t be able to reproduce. If we can’t reproduce, we’re an evolutionary dead end. It really is survival of the fittest (or perhaps survival of the healthiest).

We resist disease by means of two defence mechanisms. The first is the classical immune system, typified by the white blood cells that engulf germs, and the tiny platelets that seal up and repair injuries to blood vessels. The second defence mechanism is the behavioral immune system, which is designed to keep parasites and plagues at arm’s length. When we are disgusted by the feel of creepy crawlies on our skin, the sight of an infected wound, or the stench of rotten meat, our behavioral immune system is ordering us to maintain a safe distance.

Now, some of us have strong classical immune systems, and others have weak classical immune systems. If you’re the sort who comes down with a cold on the first day of winter, or a dose of food poisoning after catching a whiff of a day-old profiterole, you’re better off with a hair-trigger behavioural immune system. The more sensitive you are to disgusting stimuli, the less likely you are to get infected and be forced to muster your battle-weary white blood cells against hordes of invading bacteria.

Sniffing kin

Another reason for this reticence to mix with strangers is that we all have slightly different classical immune systems, with genes that are good at combating some infections but weak at dealing with others. We are more likely to share genes with people whose genetic history is similar to our own, especially family members. And this is where body odor comes in: the same genes that control immune function also influence our natural scent. It’s possible to sniff out our genetic doppelgängers!

The research

Muggleton and Fincher had ~50 men and women complete the Perceived Vulnerability to Disease questionnaire (or PVD for short), which requires respondents to agree or disagree with various statements about illness and infection. There are two types of statement in the PVD. One tests whether a respondent thinks they have a history of infection, for example: “ In general, I am very susceptible to colds, flu and other infectious diseases”. The second type of statement tests the respondent’s aversion to germs, for example: “ I prefer to wash my hands pretty soon after shaking someone’s hand.”

After completing the PVD, Muggleton and Fincher’s participants opened up eight glass jars and sniffed the contents. Inside each jar was a pad of gauze. These pads of gauze had spent 12 hours taped under a volunteer’s armpit. It’s safe to say, they stank to high heaven. Participants inhaled deeply and rated the eight pads for attractiveness, desirability, and pleasantness.

All the best psychology experiments involve a smidgen of deception, and this experiment is no exception. Although seven of the pads were provided by strangers, the eighth pad belonged to the participant him- or herself. A couple of weeks earlier all the participants had worn gauze pads under their armpits overnight, returned them to Muggleton and Fincher in sealed bags, and were led to believe that these pads were to be used in a different research project. Not so! The donors were reunited with their pads the next time they visited the lab.

Results

Muggleton and Fincher found that, among women, preference for own odor was stronger if scores on the germ aversion section of the PVD were high. That is, women who were particularly worried about coming into contact with germs tended to prefer body odors similar to their own. Women who are grossed out by poor hygiene and germ-infested handshakes may seek solace in their in-group, where people smell the same and share similar immune system genes.

However, among men the relationship between germ aversion and preference for self-similar smell was in the opposite direction. Men who were not worried about germs expressed a preference for self-similar odors.

Why should men and women differ? Both men and women can fall ill, both men and women feel disgust, and both men and women are motivated to reproduce. Surely their behavioural immune systems should function identically.

Perhaps not. Males and females evolve under distinct pressures and evolution has shaped us to respond differently to similar situations. One of the most obvious differences between the behavior of males and females is that females do most of the child-rearing (the paternal seahorse is such a striking case because nurturing fathers are a rarity in nature). As Muggleton and Fincher point out:

…in ancestral environments, females may not have the luxury of retreating
from dependent offspring. For men, we speculate that a tradeoff between kin- and self-protection can occur, such that the ancestral male eschews support, to protect close kin and other ingroup members from infection.

So, when a feller contracts man-flu, and retreats to his den for a Lemsip and a reinvigorating X-Box session, leaving his partner to tend to the kids, it’s probably because he cares.

And because his family smells awful.


Muggleton, N. K., & Fincher, C. L. (in press). The effects of disease vulnerability on preferences for self-similar scent. Evolutionary Psychological Science. Read summary

For an audio version of this story, see the 5 April 2016 episode of The Psychology of Attractiveness Podcast.

Dr. Robert Burriss

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Postdoc at Basel University, Switzerland. Evolutionary psychologist. Studies human attraction and mate choice. More at RobertBurriss.com