Sleep deprivation
We can look a lot less attractive after skimping on sleep.
In 2010, researchers from Sweden and the Netherlands took photos of people who'd slept for at least eight hours the night before and people who hadn't slept in 31 hours. Sleep-deprived people were rated as less healthy and less attractive.
Three years later, the researchers went into more detail, and other participants rated the people in the photos based on different criteria.
In general, participants said that sleep-deprived people had more "droopy/hanging eyelids, red eyes, dark circles under the eyes, and pale skin." They even looked sadder than their better-rested counterparts.
Being mean
Do nice guys really finish last?
For a 2014 Chinese study, researchers had men and women look at photos of other people, all displaying neutral expressions.
Some of those photos were accompanied by the Chinese words for "decent" and honest"; the others were accompanied by the Chinese words for "evil" and "mean"; still others weren't accompanied by any information.
Participants ended up rating people least attractive when they were described as evil and mean.
Contractive body language
The "power pose" is a controversial topic in the scientific community. A 2010 study found that expanding your body can make you feel more powerful and confident, but one of its authors recently said the effects aren't real.
But a 2016 study from researchers at the University of California, Berkeley, Stanford University, the University of Texas at Austin, and Northwestern University suggests that striking something like a power pose can make you seem more attractive — and contractive body language can make you seem less so.
In one experiment from the study above, researchers created profiles for men and women on a GPS-based dating app. In one set of profiles, the men and women were pictured in contractive positions — for example, by crossing their arms or hunching their shoulders.
In the other set of profiles, the same men and women were pictured in expansive positions, like holding their arms upward in a "V" or reaching out to grab something.
Results showed that participants were more likely to choose people in expansive postures as someone they'd like to go on a date with than those in contractive postures. And men pictured in contractive postures seemed to be at a special disadvantage.
Stress
Chill out — you might look hotter.
A 2013 study from researchers in Finland, South Africa, the UK, Latvia, and Estonia found that Latvian women with high levels of the stress hormone cortisol were perceived by heterosexual men in Latvia as less attractive.
Even though the men didn't know the women's cortisol levels (only the researchers did), it seemed to affect the women's perceived attractiveness. The researchers say that's possibly because low cortisol (and lower stress) levels indicate health and fertility.
Looking too happy or too proud
While happiness is generally considered attractive on women, girls often don't go for guys who appear overly smiley.
By contrast, while pride is typically thought of as attractive on men, guys don't seem to prefer girls who look proud.
In 2011, researchers from the University of British Columbia conducted experiments on more than 1,000 adults in North America, showing them photographs of members of the opposite sex and asking them how attractive the people in the photos were.
Results showed that men rated women most attractive when they looked happy and least attractive when they displayed pride. Women, on the other hand, rated men most attractive when they displayed pride and least attractive when they looked happy.
It's unclear, however, whether these findings on attractiveness apply across cultures. In a statement, the researchers said the results probably reflect traditional Western values and gender norms — for example, the idea that a man should look "strong and silent" and a woman should look "submissive and vulnerable."
Not having a sense of humor
A guy walks into a bar … fumbles a joke and leaves alone.
A 2009 study from researchers at the University of California, San Diego found that not being funny — and even having just an average sense of humor — is less attractive than having a great sense of humor.
The study also found that gender didn't play a role — a poor sense of humor was equally unattractive in men and women.
Laziness
The results of a series of experiments, published by researchers at the University of Wisconsin-Madison and the State University of New York at Binghamton in 2004, found that perceived attractiveness can be correlated with traits like helpfulness.
In one experiment, researchers asked students in a six-week archaeology course to rate each other on different personality traits, as well as attractiveness. They did so at the start and end of the course.
When researchers analyzed the results, they found that even students who'd been rated average at the beginning of the course were rated less attractive than average later on if their classmates saw them as lazy (for example, uncooperative and not hard working).
If you smell too similar or too different from a potential partner
Science suggests humans seek out mates who are neither too similar nor too different from them genetically — and we sometimes make these judgments based on body odor.
In a 2006 study led by researchers at the University of New Mexico, Albuquerque, for example, researchers recruited heterosexual couples to answer questions like how much they were turned on by their partners, and how many other people they'd had sex with during the course of the relationship.
Meanwhile, the researchers took DNA from the participants' mouths and brought it to a lab for testing. Specifically, they wanted to compare their major histocompatibility complexes, which are immune-system genes.
The researchers found that the more similar a couple's MHCs were, the less attracted the participants were to their partners and the more likely they were to have had sex outside the relationship.
At the same time, one study also found that we avoid partners who smell too different from us.
Dishonesty
If you're tempted to lie to make yourself seem hotter, don't.
Research suggests that dishonesty is a major turn-off for both men and women. For a 2006 study from the University of Western Ontario, participants read blurbs about men and women who were described as either intelligent or unintelligent, dependent or independent, and honest or dishonest.
Participants then rated the people they'd read about based on a number of criteria, including how much they liked them and how attractive they were.
As it turns out, honesty was the only trait out of the three to have a substantial effect on ratings of attractiveness and liking.
Heavy smoking and drinking
For a 2016 study, researchers recruited more than 200 heterosexual young women in Belgium to look at photos and bios of young men.
Results showed that men whose bios indicated they smoked frequently were considered less attractive than nonsmokers and occasional smokers — especially if the men were being considered for a long-term relationship
As for drinking, occasional drinkers were rated more attractive than nondrinkers and frequent drinkers when they were being considered for both short- and long-term relationships.
Not being humble
Immodesty can kill romance — at least according to a 2014 study from researchers at Hope College and the University of North Texas.
In two experiments, researchers had about 200 mostly heterosexual undergrads read descriptions and personality assessments of a hypothetical fellow student.
The descriptions varied — some read, "I'm a pretty good student, but not a bookworm. Other people say I'm smart, but I don't like the attention," while other said, "I'm a really good student and pretty smart, but definitely not a nerd or bookworm: I guess it just comes naturally."
When the student appeared highly humble, the undergrads were more likely to want to start a relationship with them.
If you disagree with someone's political preferences
Talk about the personal becoming political.
A 2016 paper, published by researchers at the University of California, Merced and California State University, Stanislaus suggests that our political views influence who we find attractive.
For the study, which was conducted during the 2012 presidential election, about 850 US adults indicated whether they identified more strongly with the Democratic or Republican party.
Then, participants looked at a photo and brief bio of a person of the opposite gender. In some cases, the bio indicated whether the person supported Barack Obama or Mitt Romney.
As it turns out, female Democrats found the man pictured much more attractive when he was an Obama supporter and much less attractive when he was a Romney supporter.
Men also found the woman much less attractive when she supported the opposite party. But they didn't find the woman that much more attractive when she supported the same party.
This isn't a reason to change your political affiliation so that someone finds you more attractive, of course. It's simply evidence of the myriad factors that shape our dating preferences.
