The fear of disease is associated with a preference for introverts of the opposite sex, according to a study published in the journal Evolutionary Psychological Science.

Previous research indicates that people can accurately determine whether someone is an introvert or extravert based on their facial characteristics.

The new study of 81 men and 74 women found that men who thought they were more personally susceptible to contagious disease preferred introverted female faces over extraverted female faces. Likewise, women who thought they were more susceptible to disease preferred introverted male faces over extraverted male faces.

PsyPost interviewed the study’s corresponding author, Mitch Brown of The University of Southern Mississippi, Hattiesburg. Read his responses below:

PsyPost: Why were you interested in this topic?

Brown: This study is part of a series of studies investigating how individuals perceive extraversion in other people and their decision to associate with or avoid extraverts after weighing both the potential costs and benefits of their decision to associate with them. We also wanted to know how different survival motivations contribute to what is a cost-benefit analysis, where people weigh the risks and rewards of associating with extraverts or introverts. In this study, we wanted to know what could make somebody not like extraverts as much.

Since humans are a very social animal, not liking extraverts seems to make little sense. Extraverts are friendly, want to socialize, and can provide great social support. What’s not to like? However, extraverts bring their own source of costs. They have greater physical contact with other people compared to introverts, i.e., they like to go around touching everything. That means they could also be more likely to contract infectious diseases from others and those who associate with them could potentially get sick themselves.

If you are someone who is constantly concerned about getting sick (an example from pop culture could be George Costanza), it would make sense to avoid extraverts in favor of introverts, since introverts would be less likely to have as much physical contact with other people.

We were also interested in the role of the behavior immune system, a suit of psychological and behavioral responses to disease threat to prevent us from coming into contact with infectious disease, in shaping how we form relationships with other people. Previous research has found that people become more introverted when disease is salient, which led our lab to think that if we become more introverted ourselves to prevent infection, we should also prefer people who would be less likely to transmit infection to us if we encounter them.

What should the average person take away from your study?

Individuals with greater concern of becoming infected (as measured by the Perceived Vulnerability to Disease scale) are much more likely to prefer introverted people of the opposite sex compared to extraverted people. That is, men with greater infection concerns are more likely to prefer introverted women and women with similar concerns are more likely to prefer introverted men. We can accurately perceive extraversion/introversion from a person’s face, which could mean that we may also be able to perceive what kind of behavior they may like, too. Since extraverts are more interested in casual sex than are introverts, perhaps someone with greater concerns about becoming infected may perceive extraverts of the opposite sex as more likely to have a sexually transmitted infection.

It is also important to note, too, that there was an overall greater preference for extraverted female faces compared to introverted at a level independent of disease concern. This preference did not exist for male faces. This may suggest that extraversion may have different associations in men and women. For example, although extraverts are friendly and attractive, extraverted men are physically stronger than introverted, which could possibly implicate them as greater intrasexual competition to other men and a riskier interaction partner for women.

Since there does not appear to be a relation between strength and extraversion in women, extraverted women may provide a different set of costs and benefits. Although this explanation may seem theoretically sensible, it is also necessary to conduct more research to determine the full extent of that potential explanation as well as to explore alternative hypotheses.

Are there any major caveats? What questions still need to be addressed?

Even though we found these effects with a personality scale, there were no effects based on priming individuals with ideas of disease. That means our study is ultimately correlational in the sense that we cannot say that disease concern causes people not to like extraverts. Rather, we can only say that people who already perceive themselves as vulnerable to disease prefer introverts due to a pre-existing individual difference. Although personality is a very important thing to study, our goal is determine if pathogen concern can cause individuals to dislike extraverts.

A future study would involve another disease manipulation from the one we used in our study to see if any kind of immediately activated concerns of disease could make individuals less extraverts less.

Since our effects were driven by perceptions of opposite sex faces, it would also behoove future research to consider other aspects of pathogen concern. Specifically, research should consider individual differences to disgust sensitivity based on pathogen, sexual, and moral domains. If our explanation for why there was an opposite-sex face introversion preference is true, it would seem sensible for sexual disgust to be the basis of this aversion over pathogen and moral disgust. This would not mean that disease concern is not driving the effects. Rather, it would show that a specific kind of disease concern (i.e., STIs) was driving effects instead.

Other projects considering extraverted/introverted faces should also focus on different social motives and how they may influence our desire to approach or avoid extraverts. For example, people who feel isolated may be more willing to make the tradeoff of associating with someone who could more easily get them sick if that guarantees a better chance of having friends. Our lab has investigated this concern on a dispositional level and found that motivation to fit in is associated with a greater extraversion preference.

Is there anything else you would like to add?

Our results were not necessarily perfect and several of our hypotheses were not necessarily supported in the way we planned them out to be. Nonetheless, we found some very interesting results that were in-line with our predictions that are theoretically sensible. As good scientists, we must always remember to analyze the data fully and remain persistent in trying to uncover how the world works.

In addition to Brown, the study “Avoiding Extraverts: Pathogen Concern Downregulates Preferences for Extraverted Faces” was co-authored by Donald F. Sacco.