We have never been surrounded by as many faces as we are today. In the age of social media, the brain is constantly being forced to make initial impressions of unfamiliar people. “Understanding how first impressions are formed to faces is a topic of major theoretical and practical interest that has been given added importance through the widespread use of images of faces in social media,” comments researcher Tom Hartley and his colleagues from The University of York in the journal “PNAS”. Is a person kind, unwelcoming, attractive? The brain only requires a tenth of a second to form a first impression. The researchers are of the opinion that, in this very short space of time, 65 characteristics are perceived, such as the shape of the mouth, the distance between the eyebrows or the position of the cheek bones. A lasting impression. The most astounding thing is that first impressions are mostly correct and this is proven by studies – the first impression of a person's features normally matches what the person would attribute to themselves, and this remains true even when they spend more time with that person. What changes is simply the certainty that their first impression was accurate. This was identified by American researchers Janine Willis and Alexander Todorov from Princeton University. In the brain, the amygdala is responsible for rapid emotional judgements, which explains the intuitive feeling that cannot necessarily be justified rationally. One question always plays a decisive role when forming a first impression: is my opponent trustworthy and kind or aggressive and sly? Friend or foe? Italian researcher Tessa Marzi and her team from the University of Florence came to the conclusion that this is the key question. They believe that the brain uses a sort of “toolkit” to help it work out how trustworthy unfamiliar people are. This makes perfect sense when taken from evolutionary standpoint, as there were times when the difference between friend and foe was also a decision between life and death. The brain also makes a lightning-fast estimation of a person's social status – and then decides whether or not they want to carry on interacting with that person.