The distinctive "old person smell" you may have picked up on when visiting your grandparents most likely wasn't your imagination, a new study indicates.

When given whiffs from pieces of pads worn under the armpits of young, middle-aged and elderly people for five consecutive nights, study participants could reliably distinguish the body odor of the elderly, who were 75 and older, the researchers found.

"The results of this study support the cross-culturally popular concept of an 'old person odor,'" writes the international team in a study published today (May 30) in the journal PLoS ONE.

The notion that the elderly have a distinct smell exists in multiple cultures, and usually the odor is said to be unpleasant. But this probably has more to do with negative perceptions of old age, rather than with the odor itself, according to study researcher Johan Lundström, an assistant professor at the Monell Chemical Senses Center in Philadelphia.

In the study, participants rated the smell of the elderly people as less intense and less unpleasant than the body odor of young people (20 to 30 years old) and middle-aged people (45 to 55 years old). This effect was driven by how the participants rated the body odor from men, who appeared to smell the worst and the strongest in middle age. The odor from women of all ages was rated as less intense than men, and closer to neutral smelling for the young and middle-aged.

The team used young people to do the sniffing for two reasons: They were more plentiful as volunteers and using participants from different age groups could potentially introduce a new layer of complexity, if age of the smeller influences how body odor is perceived, Lundström said.

He cautioned that while the participants did appear able to distinguish the elderly body odor, discriminating between age categories and correctly labeling odors from the elderly, they did not demonstrate a strong talent for it and showed low confidence in their abilities. [Personality Traits Affect How We Smell]

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It's not yet clear why body odor changes as humans age or why humans are able to pick up on these changes.

Body odors originate from an interaction between skin gland secretions and bacteria on our skin. As people age, the activity of different types of skin glands changes. This factor may contribute to the perceived change in body odor with age, the researchers write.

So far, scientists can only speculate on why this apparent signal for old age exists. Research in other animals indicates that such an odor may act as a sign of the "good genes" that have allowed a male to live into old age, making him more attractive to females. It's also possible the distinctive odor is not a direct result of age; for instance, it could be associated with increased inflammation (part of an immune response) within the bodies of the elderly, Lundström said.

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