If you're walking in a dark alleyway and come across a man with a short, wide face, it's best to be on your guard, suggest Canadian researchers.

A new study out of Brock University suggests men with this particular facial structure tend to be far more aggressive than a man with a smaller, narrower face.

The study, published in the Proceedings of the Royal Society B, looked at facial dimensions independent of body size. The research showed that the larger the width-to-height ratio of a man's face, the likelier he is to be aggressive.

Justin Carre, a researcher with Brock's psychology department, said men's faces tend to widen during puberty.

"Testosterone might be partly responsible for shaping width to height ratio and we know that testosterone is linked to aggressive behaviour in men -- so there might be some kind of influence in both puberty and facial structures," he said on Canada AM Thursday.

The researchers calculated the width by measuring the distance between the end of a face's left side to the other end on the right, Carre said. Height measurement was taken by calculating the distance between the brow and the upper lip.

"We divided the width by the height and that's how we got our ratio," he said.

Carre and his co-researcher Cheryl McCormick interviewed male subjects and observed male varsity hockey players and male professional hockey players. The three studies all resulted in a similar conclusion.

"In (the questionnaire), men had a larger facial width-to-height ratio, higher scores of trait dominance and were more reactively aggressive compared with women," the study said. "Individual differences in the facial width-to-height ratio predicted reactive aggression in men, but not in women."

When they observed the hockey players in both groups, the researchers found that "individual differences in the facial width-to-height ratio were positively related to aggressive behaviour as measured by the number of penalty minutes per game obtained over a season," the study said.

"Together, these findings suggest that the sexually dimorphic facial width-to-height ratio may be an 'honest signal' of propensity for aggressive behaviour."

Carre said that while some studies have shown that men with round, softer "baby faces" are more aggressive to make up for their features, his study found that it was just as important to look at the height of a face as the width of it when measuring aggression.

The correlation was strong enough to convince Carre of what to do should one happen to be walking in a dark alleyway with a stout-faced stranger.

"It's no a perfect correlation but the data suggests it might be a good idea to walk away," he said, laughing.