For years nervous exam takers and job interviewees have been advised to smile to make themselves feel better.

Sadly it seems there isn't a glimmer of truth in faking a beaming grin to make yourself feel happier and more relaxed.

For a myth-busting review of an old study reveals grinning won't always improve your mood, just as frowning doesn't make you feel unhappy.

A 1998 study asked participants to hold a pen between their teeth, causing them to 'grin', or between their lips, inducing a 'frown'.

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They were then shown cartoons and asked to rate how funny they were.

The study found those grinning were more likely to giggle at the cartoons. Its results have been cited ever since.

However, a new version of the study asked 1,900 participants to hold the pens in their mouths and complete tasks including drawing lines under vowels and between numbers, before rating the cartoons.

No evidence was found to suggest inducing particular facial expressions led people to rate the cartoons differently.

Study author Professor Eric-Jan Wagenmakers, of the University of Amsterdam, said: 'This did not replicate the results [of the original authors] and failed to do so in a statistically compelling fashion.'

The findings are published in Perspectives on Psychological Science.