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Researchers from the University of Minnesota have figured out the features of a winning smile.

  • It's a balance of the mouth's angle, smile width, how many teeth are visible and symmetry. Best bet: showing just a little bit of teeth.
  • Smiles that form slightly asymmetrically were seen as more "genuine" and "pleasant" — to a point. If it happens relatively slowly (longer than 125 milliseconds), the crooked smile just starts to get "creepy."

Why the findings matter:

  • They guide surgeries to reanimate someone's face after a stroke, says author Sofia Lyford-Pike, a facial plastic and reconstructive surgeon at the University of Minnesota. (People who are unable to smile effectively are at increased risk for depression.)
  • It could inform computer graphics.
  • More broadly, the work may help to understand how individual differences in facial expressions can lead to differences in how people perceive threats, trustworthiness and other socially relevant cues, something researchers have long studied.

What they did: The researchers created 3D computer animated faces with slightly different smiles constructed from combinations of different angles of the mouth, varying extents of the smile, how much teeth were showing and how symmetrically the smile formed on the face. 802 people were then asked to rate 250 millisecond-long video clips of the smiles forming for their effectiveness, how genuine they seemed, whether they were "pleasant" or "creepy," and what emotion they thought the smile conveyed. The best-rated smiles have lips angled between 13 and 17 degrees and extend between 55% and 62% of the distance between the eye's pupils.

Two smiles with a combination of (a) smaller and (b) larger mouth angle-smile width combination. Increasing how much teeth are visible led to a more favorable rating of the smile in (b) and a worse rating for (a).Helwig et al. University of Minnesota

Limitation: The study only modeled the mouth. Previous work has found the eyes influence people's perceptions but the study shows the mouth can transmit a lot of information on its own, says Lyford-Pike.

What's next: Determining whether the results translate to spontaneous smiles of different, real people, is a key question, says Aleix Martinez, a cognitive scientist and professor of electrical and computer engineering at Ohio State University. Martinez asks: "Can you predict a person's success (personal, profession) on the "niceness" of their smiles?"

Go deeper

Updated 14 mins ago - Health

2 federal judges temporarily block Biden vaccine mandates

President Biden delivers remarks on the Omicron COVID-19 variant at the White House on Nov. 29. Photo: Anna Moneymaker via Getty Images

The Biden administration was temporarily blocked from enforcing COVID-19 vaccine mandates for millions of workers by federal judges in two states on Tuesday.

The big picture: The orders, by federal judges in Kentucky and Louisiana, come one day after a federal judge in Missouri halted the mandate, which has a Jan. 4 deadline, in 10 states.

45 mins ago - World

Honduras elects first female president

Honduran President-elect Xiomara Castro, of the Libertad y Refundacion (Libre) Party, in Tegucigalpa, Honduras, on Sunday. Photo: Inti Ocon/Getty Images

Former Honduras first lady Xiomara Castro is set to become the country's first female president president, after the ruling party conceded defeat in the country's elections on Tuesday night, per AP.

Why it matters: The democratic socialist and her Libre Party have broken a 12-year run for the conservative National Party, which U.S. prosecutors alleged fostered a "narco-state," note Axios' Latinos' Marina E. Franco and Russell Contreras.

Food delivery "ghost kitchens" face major obstacles

Photo: Jakub Porzycki/NurPhoto via Getty Images

The growing popularity of food delivery has given rise to startups that open "ghost kitchens" — kitchens in warehouses or trailers that prepare food solely for delivery and have no option to dine in.

  • But they can come with a whole host of problems.

The big picture: The concept of "ghost kitchens" has been dubbed the next big thing in the future of services, with high profile backers like Uber founder Travis Kalanick. But these kitchens can be hard to run or unsafe.