A single photograph can detect a person's biological age and their chance of surviving cancer, researchers say.
Experts from Mass General Brigham in Massachusetts have developed an AI tool trained on more than 40 million pictures to determine key indicators of a person's health.
The cancer estimates were then checked against real patient data to verify their accuracy, the authors said.
Biological ageing refers to how old the body is in terms of health and function rather than the number of years a person has lived.
Hugo Aerts, professor at Harvard University and director of the AI in medicine program at Mass General Brigham, said the new work "advances the field of facial health recognition AI a step further by learning survival risk directly from facial photographs of patients with cancer".
"To our knowledge, this is the first demonstration that an AI model can directly predict cancer survival from a simple photograph."
The researchers found that how people live their lives also influences ageing in the face, with heavy alcohol use, drug use and smoking associated with looking biologically older.
Smoking showed the strongest pattern, with smokers looking older than former smokers, and former smokers looking older than people who never smoked.
Raymond Mak, associate professor of radiation oncology at Harvard Medical School, said the team was surprised by how consistent the study's findings were "across common real-world photo variations, including pose, lighting, facial expression and makeup".
"Our goal is to make face photograph-based health assessment more quantitative, consistent and scalable so it can support personalised treatment decisions rather than replace physician judgment."
The study was published in Lancet Digital Health.