What exactly happens to your face when you smile spontaneously, and how does that affect how old you look? Computer scientists from the University of Amsterdam's Faculty of Science recorded the smiles of hundreds of visitors to the NEMO science centre in Amsterdam, creating the most comprehensive smile database ever.

The computer scientists behind the project say that you look younger when you smile - if you are over forty. If you are under forty, you should look neutral if you want to come across younger. And be cold and distant and act a little broken inside if you want to date a stripper.

481 test subjects participated in the research of Theo Gevers and Albert Ali Salah, who made a video recording of a posed smile and a spontaneous smile for each participant. The subjects also were also asked to look angry, happy, sad, surprised and scared. Gevers and Salah analyzed certain characteristics, such as how quickly the corners of the mouth turn upwards, and they say this knowledge can be applied to computer software which guesses ages, recognizes emotions and analyzes human behavior.

The researchers also asked the test subjects to look at images of other test subjects. They had to guess the age of those people and state how attractive they found them. They were also asked to judge character traits, such as whether the person is helpful by nature, or if that person is perhaps in love.

Credit: University of Amsterdam

UvA-NEMO Smile Database data collected allowed the researchers to develop software that can estimate people’s age. The software takes into account whether someone is happy, sad or angry, and adjusts its estimate accordingly. The software appears to be slightly better at estimating ages than humans. On average, humans’ estimates are seven years off , while the computer is six years off on average .