The expression on someone’s face is not a sure-fire way to determine their trustworthiness, University of British Columbia researchers say.

A study conducted by UBC Psychology professor Stephen Porter and PhD student Alysha Baker found people often make judgements of trustworthiness based solely on the physical appearance of the face - rather than the expression used.

"Our findings in this and our past studies suggest that your physical appearance can have major implications for your assumed credibility and other character traits, even more powerful than the manner in which you behave and the words you speak," Mr Porter said in a statement.

"The implications in social, workplace, corporate and criminal justice settings are enormous."

Researchers asked participants in the study to watch a video, listen to audio-only pleas or examine a photo of people publicly asking for the return of a missing relative. They then asked for their personal perceptions of general trustworthiness and honesty.

There are certain facial features considered that make an individual look more trustworthy--higher eyebrows, more pronounced cheekbones, rounder face--and other features that are perceived to be untrustworthy-looking--downturned eyebrows, or a thinner face,” said Ms Baker, who conducted a large amount of the research.

The study illustrates this with two real criminal cases. An 81-year-old woman was accused of killing her husband but people believed her public appeal for justice, even thought it was later determined she did kill her husband.

But the father of a missing girl was judged by many to be lying based on his facial features, even though later he was proved innocent.

Ms Baker believes that in some legal settings those who are deemed untrustworthy-looking may be judged more harshly than those who are judged trustworthy-looking.

In the United States, untrustworthy-looking men are more likely to receive the death penalty than trustworthy-looking men convicted of similar crimesm, according to Ms Baker.

"When encountering a person in any given situation, we automatically and instantaneously form an impression of whether a target is worthy of our trust because, evolutionarily, this kind of assessment has helped our survival. For example, assessing 'friend or foe'," Baker said.

She added: "We're typically not aware of this quick decision and it may be experienced as 'intuition', but this can be particularly problematic in the legal system because these first impressions are often unfounded and can lead to biased decision-making."