If you're happy and you know it there are a lot of reasons to show it. Past studies have found that smiling people are deemed to be friendlier, more attractive, and more memorable than people with neutral facial expressions.

However, a new study published in the Psychonomic Bulletin & Review reveals a somewhat surprising effect of smiling: It makes you look older.

When Dr. Tzvi Ganel, a professor of psychology at Ben-Gurion University in Israel, looked to tackle the subject, he was surprised to find it relatively untouched. Just one study had been conducted, which asked participants to rate the age of people depicted to be angry, fearful, disgusted, sad, neutral, or smiling. Unsurprisingly, smiling people were judged to look younger than those who were angry, fearful, sad, or disgusted. There were no age differences between smiling expressions and neutral expressions, however.

Ganel saw shortcomings in the study's design.

"It is difficult to interpret these findings due to the fact that the experimental design included repeated presentations of photos of belonging to the same persons bearing different expressions. This may have biased overt age evaluations," he noted.

So Ganel sought to carry out a study that corrected the problems of the first. Across three experiments, sixty participants were shown pictures of 220 men and women with either neutral or smiling facial expressions and asked to estimate the age of the depicted men and women.

In every experiment, smiling faces were deemed to be older, and the differences were highly statistically significant.

"When people smiled, they were perceived as between 1 year to almost 2 years older than when they were presented bearing a neutral expression," Ganel described.

Ganel next sought to find out why. He noticed that smiling amplifies the appearance of wrinkles, particularly around the eyes, so he conducted another experiment, in which twenty participants estimated the age of people with smiling or neutral expressions in photos altered to make wrinkles more apparent (b) and twenty others estimated the age of people in photos altered to conceal wrinkles (c). Ganel found that when wrinkles were hidden, smiling individuals were no longer estimated to be older.

The study suffered from a couple of the usual limitations that plague psychology experiments. The participants rating the photographs were all college students, and the photographs were all of people aged 20 to 40. Thus, it is unknown if the effect will persist among older subjects, with facial wrinkles that are more pronounced and ubiquitous. Ganel has plans to fix both of these limitations in future studies.

Source: Tzvi Ganel. "Smiling makes you look older." Psychonomic Bulletin & Review. 9 Apr. 2015. DOI: 10.3758/s13423-015-0822-7

(Image: AP)