The adverts (and Kanye West) have got it wrong – an emotional expressionless face isn't the epitome of cool, but smiling is!

That's according to researchers in the US who challenged the idea that concealing emotions was perceived as cool.

This message is reinforced through advertisements where fashion models rarely smile and by quotes from celebrities.

In an article in the Huffington Post, Kanye West said he doesn't smile in photographs because 'it just wouldn't look as cool'.

In a series of experiments, researchers at the University of Arizona showed participants photographs of celebrities and non-celebrities who were smiling or inexpressive, and their results call into question common assumptions about what makes someone cool.

They reveal: 'We found over and over again that people are perceived to be cooler when they smile compared to when they are inexpressive in print advertisements. Being inexpressive makes people seem unfriendly or cold rather than cool.'

The researchers asked participants to view print advertisements for a clothing brand, and the model in the ad was either smiling or not.

The models included well-known celebrities, such as James Dean, Emily Didonato and Michael Jordan as well as unknown models, and they were endorsing unfamiliar brands and well-known brands.

Then the participants rated the extent to which the model seemed cool on a seven-point scale. The participants consistently rated the smiling models as cooler than the inexpressive models.

Warren was surprised that participants preferred the smiling pictures of James Dean, who is typically inexpressive in photographs and considered a cool icon.

The study also showed that participants had a less favourable impression of the brand when the models were inexpressive.

The only exception was in competitive situations. When a news article showed mixed martial arts fighters who were going to face one another at a press conference, participants rated the inexpressive athlete as more cool and dominant than a smiling athlete. When the context changed to a friendly meeting with fans at a press conference, then the participants rated the smiling fighter as cooler.

The findings not only have implications for advertisers who are striving to make favourable impressions with consumers, but also for people as they relate to one another.

It may also have impact on aesthetic dentistry and a new understanding of the importance of a healthy smile.

The study is available online in the Journal of Consumer Psychology.