Is beauty only skin deep? Children don't seem to think so, like adults and babies, children think the uglier you are, the less trustworthy you are.

In a study recently published in Frontiers in Psychology, researchers have found that as children, how we perceive someone's trustworthiness is linked to how attractive we find them. Our ability to make this trustworthiness judgement develops as we grow, becoming more consistent as we approach adulthood, and, girls are better at it than boys.

Many psychology studies have proven the existence of the so-called "beauty stereotype." This describes the phenomenon whereby more attractive people are also considered to be smarter, more sociable and more successful. To be attractive is to be treated better by your peers, and preferred by new-born babies, than uglier people.

People use facial cues to make judgements on a person's character -- and this ability to infer social traits is a crucial part of social functioning and development. Although well researched in babies and adults, the development of this ability in children was not previously known.

Understanding this process paints a more complete picture of this development from birth through to adulthood. It also adds to a growing body of work showing that attractiveness is a universal language when it comes to that all-important first impression.

Dr Fengling Ma and Dr Fe Xu of Zhejiang Sci-Tech University, and Dr Xiaming Lu of Wenzhou Medical University, China, assessed 138 participants -- groups of children aged eight, ten and 12 years old, and compared them to a group of adults.

They used a face generation program (FaceGen) to produce 200 images of male faces -- all with a neutral expression and direct gaze. In the first of two sessions, each participant was shown each face, and asked to rate how trustworthy they thought that person was. A second session followed a month later where participants repeated the exercise, this time rating the attractiveness of the same faces.

The study analysed the responses of the children and adult control groups. The researchers looked firstly at the ratings of trustworthiness, and level of agreement of the ratings within and between the groups. Did the children within the same age groups agree on how trustworthy each of the faces was?

Did the responses of the different age groups agree with each other, and with the adult group? They found that the level of agreement within and between the age groups and the adult group increased with age. From this they were able to infer that the children's ability to judge trustworthiness therefore also increased with age.

Next, the researchers looked at the ratings of trustworthiness and attractiveness given to each face. They found a strong, direct relationship between the two traits -- the faces deemed more trustworthy were also considered to be more attractive. This relationship also strengthened with age, and reveals that, like adults, children also look to a person's attractiveness as an indication of their character.

So, it appears that judging a book by its cover, however incorrectly, is something we are born to do and only increases with age.