It is the most important part of a woman's day. But for many, all that work with the blusher and lipstick could be a waste of time.
Make-up, scientists believe, interferes with the most basic and instinctive lines of communication between male and female. It masks the natural feminine glow which, through centuries of evolution, has been the signal to a man that a woman is fertile.
Previous studies have suggested that men who are fertile have more attractive faces.
In the latest research, scientists at St Andrews University established a similar pattern in women - and then looked further to examine the effect cosmetics have on this gift of nature.
They found that make-up could improve the appearance of the less attractive woman, thus confusing the instincts of the male into thinking she was more fertile than she actually was.
But on the good-looking woman, it did not improve her chances of attracting a partner. She would be just as successful relying on her natural beauty.
Student study
The researchers took 56 female students, photographed them over four weeks and also monitored their levels of the hormones oestrogen and progesterone, which are key indicators of female fertility.
They used a computer to morph faces into composite photographs of women with high fertility and others of those with low, then showed them to a panel of men and women and asked them to say how attractive each woman was.
The high-hormone composites were universally preferred, thus proving the link between beauty and fertility. They then showed the panel the true faces of the volunteers, some of whom wore make-up and others who did not.
Among those not wearing make up, the ones with higher levels of oestrogen were significantly more likely to be considered attractive.
They were also rated as more feminine and healthy.
Among those with make-up, the pattern was lost and the results far more random, suggesting that the cosmetics acted as a leveller, cancelling out the natural advantage of the attractive volunteers.
The study, published in the journal Proceedings of the Royal Society B, concluded: "The use of make-up may compensate for or mask cues indicating low hormone levels."
Research leader Miriam Law Smith said oestrogen had an impact on appearance during puberty, when it can affect bone growth and skin texture. Those with high levels often have attractive bone structure and smooth skin.
"Women are effectively advertising their general fertility with their faces," she said.
"Our findings could explain why men universally seem to prefer feminine women's faces.
"In evolutionary terms, it makes sense for men to favour feminine fertile women - those that did would have had more babies."
The finding fits with research earlier this year which found that women who spend thousands of pounds a year on make-up could be wasting their time. In a poll of 10,000 single men, 68 per cent preferred natural beauty to women who were plastered in cosmetics.
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