Forget the botox and hair dye - people can smell your age, a study has shown.
In tests, volunteers were able to distinguish between young, middle aged and elderly individuals by sniffing their body odour.
But contrary to popular conception, "old person smell" was rated less intense and unpleasant than other age group odours.
Scientists collected armpit odour samples from three groups of 12 to 16 donors aged 20 to 30, 45 to 55, and 75 to 95.
Donors were asked to sleep for five nights in T-shirts containing underarm pads which were cut up and placed in glass jars.
These were assessed by 41 "evaluators" aged 20 to 30 who were given pairs of glass jars in different combinations to sniff.
On each occasion, they had to decide which jar contained samples from the older donor.
They were also asked to rate the intensity and pleasantness of each odour.
Evaluators were able to discriminate between the three donor age categories, the researchers reported in the online journal Public Library of Science ONE.
"Similar to other animals, humans can extract signals from body odours that allow us to identify biological age, avoid sick individuals, pick a suitable partner, and distinguish kin from non-kin," said lead researcher Dr Johan Lundstrom, from the Monell Chemical Senses Centre in Philadelphia, US.
In the animal world, age-related odours are believed to guide mate selection. Older males might be desirable because they contribute genes linked to longevity, while older females with fragile reproductive systems may be avoided.
A unique "old person smell" is recognised across human cultures. In Japanese it even has a special name, kareishu.
Dr Lundstrom said: "Elderly people have a discernible underarm odour that younger people consider to be fairly neutral and not very unpleasant.
"This was surprising given the popular conception of old age odour as disagreeable. However, it is possible that other sources of body odours, such as skin or breath, may have different qualities."
Body odours originate from a "complex interaction" between skin gland secretions and bacterial activity, the researchers wrote.
Skin gland composition and secretion were said to change in "age-dependent manner throughout development".