As many women can testify, there's a fine line between pretty and scary when it comes to make-up.

Now, scientists have shown that not only does the right amount of cosmetics make all the difference when it comes to beauty, but it also affects judgements of competence and trustworthiness.

For all of their positive effects on looking and feeling good, large amounts of make-up soon start to negatively impact on the way people perceive an individual's honesty.

In the study, funded by Procter & Gamble, scientists at Massachusetts General Hospital, Harvard Medical School, Boston University and the Dana-Farber Cancer Institute asked participants to rate various looks in terms of competence, likeability, attractiveness and trustworthiness.

Pictures of women wearing no make-up, and looking 'natural', 'professional,' and 'glamorous,' were shown to volunteers for different lengths of time.

When shown the images for just 250milliseconds, all ratings went up with the amount of make-up, says the report, published by Plosone.org.

However, when study participants were allowed to take in the pictures at length, the results changed significantly.

Nancy Etcoff, the study's lead author and associate researcher at Massachusetts General Hospital told ABC news that 'we found that when faces were shown very quickly, all ratings went up with cosmetics in all different looks.'

'The women were judged as more competent, likeable, attractive and trustworthy.'

Given more than just a glimpse of the images, participants showed that beauty and competence went up, but trustworthiness - or honesty - soon suffered as cosmetic looks became heavier.

'When they got to the more dramatic make-up looks, people saw them as equally likeable and much more attractive and competent, but less trustworthy,' comments Etcoff to the news site.

(Read by Christine Mallari. Christine Mallari is a journalist at the China Daily Website.)

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(Agencies)