John Krasinski is the Sexiest Man Alive — but what makes someone sexy in the first place? Here's what science says.

Each year, People magazine crowns a Sexiest Man Alive, and while the title often comes with plenty of debate (no Ryan Gosling? seriously?), there's no doubt that past winners like Channing Tatum and Michael B. Jordan, and this year’s John Krasinski, have far more sex appeal than the average Joe.

Sexiness, however, isn’t always something you can tap into just by looking at someone. And there are even scientific reasons behind why someone might be deemed more attractive than the next person. Here’s what we know about what makes for a sexy human.

Symmetrical faces are desirable — and so are clearly masculine or feminine ones

You may have heard that one way to deem someone’s attractiveness is by how evenly matched both sides of their face are. One theory was that symmetrical faces might indicate better health, therefore making us subconsciously deem that person as a better fit to carry down our genes. Research from Brunel University London in 2014, however, suggested that is likely not the case, and that it’s possible that humans prefer symmetrical faces the way we prefer symmetry in art and design.

But there’s another factor to consider as well: According to 2017 research from Oakland University in Michigan, straight men were more attracted to faces that were deemed more feminine, while straight women were more into faces that appeared more masculine. This was true even when the faces were less symmetrical — and less healthy in appearance — than they were masculine or feminine.

Funny people are sexy

There may be an amusing reason why guys like Paul Rudd and Ryan Reynolds have been crowned People’s Sexiest Man Alive. A 2017 research study — which used speed dating as a methodology — found that people who were deemed funny were also considered more attractive than they were when initially rated by researchers, who were at first unaware of their sense of humor.

Conversely, the same research showed that the people who were found to be not funny were also described as less attractive.

Your genes may be sexy

That may at least be true when it comes to finding a partner. Sara Seabrooke, co-founder and chief scientific officer at Instant Chemistry, told Yahoo Life in 2016 that genes of our immune system contribute to how physically attractive someone seems to us. That's because these genes contribute to our body’s scent, and “the better the person smells to us, the more likely they are to be biologically compatible.”

In addition to biologically compatible partners finding one another more attractive, they also tend to have more satisfying sex lives and greater stability in their relationship, Seabrooke explained.

Playing 'hard to get' is sexy — up to a point

Research from the University of Rochester, published in the Journal of Social and Personal Relationships in 2020, found that playing “hard to get” increases a person’s desirability. One theory is that people want to date someone of the highest mate value possible, and if someone is a bit too eager, that may read as unattractively desperate.

There is, however, a delicate balance: Previous research also found that people who believed their potential partner was interested in them put more effort into seeing the person again, compared to when they were uncertain about their affection.

The key, per the study’s co-author Harry Reis, may be to hold back on what information you share about yourself in order to build a sense of anticipation — this, as opposed to coming off as disinterested or arrogant.

Surprising personality traits make people sexy — but it differs depending on where you live

A 2015 survey of 10,000 men and women across the globe found that traits like vulnerability, courage, individuality and honesty were considered highly attractive. What trait was ranked highest depended on who was surveyed. Europeans cared most about compassion, Asians cared most about spirituality, and Australians considered courage most significant. North Americans found ambition to be the hottest trait.

This article was originally published on Nov. 8, 2023 and has been updated.