Can you guess the ages of these faces?

Humans are awful at estimating a person’s age based on their face alone. This can lead not only to uncomfortable social situations, but also to critical errors in criminal investigations and enforcing age-based restrictions on such things as alcohol and gambling. New research shows people are usually off by about 8 years, and their estimate might be shaped by the last face they saw.

To conduct the study, researchers collected 3968 pictures of consenting participants from the Australian Passport Office—31 men and 31 women at each age from 7 through 70. Then, they showed 81 people photographs of a man and woman at each age in a random sequence, and asked them to guess their ages. The faces above are computer-generated averages of more than 100 pictures from the study of people aged 19 to 22, 50 to 53, and 63 to 66.

Volunteers consistently guessed that young faces were several years older than they actually were and that older faces were several years younger than they actually were, the team reports today in Royal Society Open Science. The results also showed that people’s estimates were affected by the previous face they had viewed—if they had just seen a young face, they usually lowballed the next face’s age, and vice versa.

The researchers hope their results can be used to develop “mental palate cleansers” for people like security guards who have to review multiple faces one after another. Looking at a distorted image of a face or taking a longer pause in between faces in a series could help eliminate this carry-over effect.