Actress Scarlett Johansson uses her pout to full effect
Women who have fuller and firmer lips are seen as younger than they really are, research suggests.
Even with a few wrinkles or grey hairs, a plump pout can takes years off a woman, Unilever scientist David Gunn has found.
His study of over 250 women, including sets of twins, reveals that thin lips are a genetic trait rather than a result of our environment.
The findings are published in PLoS One journal.
The researchers found a large variation in lip thickness among women over 60.
The pink part of the thinnest lips measured just 3mm from the top of the upper lip to the bottom of the lower lip, while the fullest lips among the over-sixties measured 2.2cm.
Other tell-tale signs of ageing that appeared to be genetically determined included a receding hairline and greying hair.
But wrinkles, sun damage and age spots were equally influenced by both genetic and environmental factors.
Researcher David Gunn said: "When we identified people who looked young for their age, we were struck by the difference in their lips.
"It is a feature that is strongly genetically determined and relatively easy to measure."
Experts know that lips reach their maximum volume in young adulthood.
For many people, they begin shrinking between the ages of 30 and 40, and can make a person look older than they really are.
Although surgery and botox can be an effective way to increase the size of your lips, experts are divided over whether it makes a convincing difference.
There can also be disadvantages to collagen or silicone implants.
Actress Leslie Ash suffered long-term damage to her lips, earning her the nickname "trout pout", when her implant surgery went wrong.
Mr Gunn said there was little to be gained by thin-lipped middle-aged or elderly women seeking lip implants.
He said: "It just looks odd because it doesn't counter the impact of a wrinkled face."