Beauty really is skin deep. Scientists have found that the evenness and radiance of a woman’s skin is the key factor people use in judging beauty and attractiveness.

The findings suggest that an even skin tone is much more important than the symmetry of a face — a quality which had previously been thought the most important aspect in deciding attractiveness.

One experiment showed that people were much less willing even to look at someone with uneven skin tone, regularly averting their eyes.

The scientists behind the research suggest humans have developed an acute awareness of skin tone because it is a powerful indicator of health and reproductive fitness.

“Skin tone, especially in women, says a great deal about reproductive potential,” said Dr Bernhard Fink, an expert in evolutionary psychology at the University of Göttingen in Germany.

“Humans are highly evolved to pick up on cues like that because at one time in our past it would have been crucial for reproductive success.”

Such findings could help explain the continuing success of older actresses like Halle Berry, 43, and Cate Blanchett, 40 — both are renowned for having “good skin in close-ups”.

Fink will discuss his research in a lecture at the Royal Institution in London later this month. He believes the evolution of attraction helped determine some of the physical differences between men and women.

Scientists researching the relative importance of factors in facial attractiveness such as skin tone and symmetry had previously found it hard to separate them out.

They overcame this by using computers to create idealised images of people’s faces or bodies. This allows researchers to alter single factors such as symmetry and then ask people to score the images for attractiveness.

Fink and Dr Paul Matts, a skin researcher at Procter & Gamble’s cosmetics division in Egham, Surrey, suspected that skin tone would produce an even sharper reaction and devised a similar technique to test the idea.

They photographed 170 women’s faces, aged 10-70, applied their skin to an idealised computer model and asked 430 people to score them for attractiveness. This meant the only variable was skin quality. Matts said: “The highest scores went to the models with the most even skin tone. It seems to be more important than almost any other factor.”

In another study, they photographed women aged 50-plus. Those with wrinkles were perceived as older but not necessarily unhealthy, while those with uneven skin tone were seen as showing age and poor health.

Additional reporting: Jack Losh

Times Recommends

• Please help: maimed children of war want their lives back
• Unlocking the cruellest prison
• Charles named in £81m court battle