While smiling is host to a bevy of benefits: It releases endorphins, strengthens your immune system and makes you more approachable, new research has determined that smiling comes with a crucial deterrent: it makes you look older. Approximately two years older, in fact.

To reach this result, researchers flashed images of people each sporting three different expressions: smiling, neutral and surprised to a group of 40 participants. To everyone’s astonishment, people believed that subject’s who were smiling looked the oldest.

“We associate smiling with positive values and youth,” the study’s co-author Melvyn Goodale says. “Think of all the skin-care and toothpaste companies that sell the same idea every day.”

Contrary to popular opinion, the aging effect of a smile causes wrinkles or “laugh lines” to form around the eyes and mouth. These wrinkles cannot be ignored, the researchers add. Subjects who appeared surprised in the images were perceived youngest, as the expression tends to smooth facial wrinkles.

“When people look surprised, their brows may furrow, but that’s not what people are noticing,” Goodale tells Yahoo Beauty. “They’re staring into your eyes and the surrounding wrinkles. And the harder you smile, the more lines you’ll have around the eyes.”

I also can’t help but draw the comparison to a face injudiciously treated with Botox, in which one’s eyebrows appear a mere inch or so under the hairline, thereby sporting an expression of constant, unceasing and sometimes inexplicably creepy surprise. This makes people look older, but mostly because you can tell they’ve used a filler.

Here’s where things get a little weird: Though people believed smiling made people look older when confronted by physical images, their steadfast belief that a happy face is directly associated with one’s youth was at odds with and actually outweighed their earlier observation.

“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,” Goodale says. “They were completely blind to the fact they had ‘aged’ the happy-looking faces. Their perceptions and their beliefs were polar opposites.”

If age lines don’t bother you, research from 2013 found that smiling makes a person look clever and attractive. So while sporting a gracious grin may contribute to an aged appearance, it won’t necessary make you any less attractive.

So keep expressing yourself any way you want and remember: It takes 43 muscles to frown, but only 17 to smile.