"We associate smiling with positive values and youth. Think of all the skin-care and toothpaste companies that sell the same idea every day," said Melvyn Goodale, from the University of Western Ontario in Canada.
Researchers flashed images of people with smiling, neutral and surprised expressions to the participants.
They found that participants perceived the surprised faces as the youngest and smiling faces the oldest.
"The striking thing was that when we asked participants afterwards about their perceptions, they erroneously recalled that they had identified smiling faces as the youngest ones," said Goodale.
The ageing effect of a smile stems from people's inability to ignore the wrinkles that form around the eyes during smiling. A look of surprise, on the other hand, smooths any wrinkles, researchers said.
"It may seem counter-intuitive, but the study shows that people can sincerely believe one thing and then behave in a completely different way," Goodale said.
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