We’ve always been told to watch out for those laugh lines, but apparently a smile can make you look younger right now, if not in the future. A new study shows that people are more likely to underestimate the age of a person with a happy expression.

The German study asked its 154 volunteers of all ages to examine photographs of faces with angry, fearful, disgusted, happy, sad and neutral expressions, and guess the ages of the photo subjects. The initial goal of the study was to find out how well people estimated age across the adult life span.

The findings showed that study volunteers in every age group tended to underestimate the age of happier faces, while they overestimated the age of faces with more negative expressions. The neutral faces were guessed most accurately.

“Our study is the first to show that facial expression affects both accuracy and bias in age estimation,” said lead author Manuel Voelkle, a research scientist at the Max Planck Institute for Human Development in Berlin.

Voelkle also theorized that happy faces are misleading because they cause the face to wrinkle, which makes it difficult to tell how much the face would be wrinkled when not smiling. He also said that a smiling face probably has a halo effect, meaning people usually perceive a grinning person to be more attractive, more positive and younger.

The study also found that older volunteers were less accurate at correctly guessing someone’s age, and that younger people tended to underestimate a person’s age, while older people seemed to overestimate them.

The results of this study do seem to justify new photo ID standards requiring neutral expressions and no smiles, since faces with expressions are more likely to throw off age estimations.

[MSNBC]