Faces have long been assumed to age uniformly, but new research suggests that different areas become physiologically old at different times.
Scientists from UT Southwestern Medical Center found that the rate of ageing varies between the 'fat compartments' of the forehead, cheeks, eyes and mouth.
Dr Rod Rohrich, chairman of plastic surgery and senior author of the study, said: "This is a revolutionary way of viewing facial anatomy.
"It not only tells us how we age, it shows us why we age the way we do, and why every part of the face, from the eyelids to the cheeks, ages differently."
He added: "This will help plastic surgeons around the world not only understand how we can better rejuvenate the face, but how people age as a physiological process."
A youthful face is characterised by a smooth transition between fat compartments. As people age, the compartments lose volume in certain areas and gain it in others, which can result in sagging or hollowed skin and wrinkles.