Women find men less attractive when they smile compared to when they take on swaggering or brooding poses, a Canadian study has found.

In contrast, men find women more attractive when they smile, and least attractive when they look proud and confident, the study of 1,084 heterosexual men and women shows.

"Generally, the results appear to reflect some very traditional gender norms and cultural values that have emerged, developed and been reinforced through history, at least in Western cultures," Jessica Tracy, a sociologist at Vancouver's University of British Columbia, said in a statement Tuesday.

She co-authored the study with psychology graduate student Alex Beall. Their results were published online Tuesday in the journal Emotion.

While previous studies have shown that women are judged more attractive when they smile, the researchers believe this is the first study to show that men are judged less attractive when they appear happy.

They suggested it was because smiling men were judged to be more feminine and less dominant.

The study "helps to explain the enduring allure of 'bad boys' other iconic gender types" and may "inspire online daters to update their profile photo," said a news release about the study.

'Gut reactions'

Beall noted that the study explored first impressions and did not ask whether they thought the people in the photos would make a partner or spouse.

"We wanted their gut reactions on carnal, sexual attraction," he said in a statement.

The paper said one important question for future research is to find out whether the effects seen in judgments from photographs can be seen in live social interactions.

The study took place in two stages.

In the first, a research assistant showed about 100 study participants photographs of the same member of the opposite sex in four poses:

Happy (smiling).

Proud (with arms raised overhead).

Ashamed (with eyes downcast).

Neutral (staring straight ahead, expressionless).

Participants were asked to rate the person's attractiveness on a scale of one to nine, where nine was the most attractive.

In the second stage, study participants were shown photographs online. The volunteers were divided into three categories:

340 Canadian undergraduate students with a median age of 20, who were shown a set of 40 photos of the opposite sex.

120 North American adults with a median age of 39, who were each shown 40 photos of men and 40 photos of women.

About 400 Canadian undergraduates, who were shown the same set of photos as the older adults.

The photos were categorized into the same four categories — happy, proud, ashamed and neutral — by research assistants who did not know why the photos were being categorized. The study participants were asked to rate the attractiveness of the people in the photos.

In all cases, men rated "happy" women highest — above five on the scale. Proud women were rated on average one to two points lower, and were rated lowest among those shown the online photos.

Women consistently rated the proud men highest, with a rating of four to five. They rated happy men about one point lower. Younger women rated happy men lowest, while older women tended to rate happy and ashamed men equally and neutral men lower.

The researchers suggested that shame was considered somewhat attractive in both genders because it expresses respect for social norms.