A person's facial expressions and mood can be misperceived due to differences in facial features such as eyebrow shape, eyelid position and wrinkles, according to a U.S. study.

It included 20 health care workers who viewed photos that were digitally altered to change a number of features. The participants were asked to rate, on a scale of 0 to 5, seven expressions or emotions conveyed in the photos: tiredness, happiness, surprise, anger, disgust, fear and sadness, United Press International reported.

Results for the altered photos were compared to the scores from the original photos. Overall, eyebrow shape was deemed to be the greatest indicator of mood, drooping of the eyelids was considered the biggest indicator of tiredness, and raising the lower eyelid and the presence of crow's feet were associated with happiness.

The study appears in the journal Plastic and Reconstructive Surgery.

"A key complaint of those seeking facial plastic surgery is that people always tell them they look tired, even when they do not feel tired," study co-author Dr. John Persing said in a prepared statement cited by UPI. "We found that variations in eyebrow contour, drooping of the upper eyelid, and wrinkles may be conveying facial expressions that don't necessarily match how patients are feeling."