(Photo: Nicolas Holzheu via Flickr/Creative Commons)

(Photo: Nicolas Holzheu via Flickr/Creative Commons)

People can tell how old you are by how you smell, according to new research published in the journal PLoS One.

It appears that “old person smell” some people complain about is for real, that elderly people emit a unique identifying odor.

An elderly individual’s “old person smell”  is actually acknowledged and accepted in cultures throughout the world.  In Japan, there’s a special word, kareishū,  that describes it.

Funny thing though, according to the research, all age groups rated “old person smell” as less intense and less unpleasant than the body odors of middle-aged and young individuals.

Our sense of smell, coupled with our unique body odor, provides us with a very powerful and effective method of non-verbal communication.

The body odors of other, non-human animals, hold a wide assortment of a number of chemical components that can communicate a wide variety of social information.  Scientists say that the intensities of the chemical behind those odors and how they are perceived by others tend to change throughout a person’s life.

“Similar to other animals, humans can extract signals from body odors that allow us to identify biological age, avoid sick individuals, pick a suitable partner and distinguish kin from non-kin,” said Johan Lundström, senior report author, who is a sensory neuroscientist at the Monell Chemical Senses Center in Philadelphia, Penn.

Scientists have theories regarding how these age-related odors relate to mating and how they help animals choose their suitable mates.  For example, certain scents might suggest that older males are more desirable because they contribute genes that allow offspring to live longer, while older females might be avoided because their reproductive systems are more fragile.

In conducting the research for the study, scientists collected samples of body odor from people in three age groups. Those between 20 and 30 years old were considered to be the young group, those 45 to 55 were the middle-age group and the old age group was made up with people between 75 and 95 years-old, with 12 to 16 people per group.

Each test subject slept in an unscented t-shirt that contained underarm pads for five nights.  These pads where then cut into four pieces and placed into separate glass jars.

A group of 41 young (20 to 30 years old) people served as evaluators and were each given two of the test jars in nine combinations and were asked to identify which of the samples came from older people and evaluate the odors based on  intensity and how pleasant each one was.   These young evaluators were then asked to give an estimate as to the age of the donor of each sample.

The evaluators were able to differentiate people in each of the three donor age groups based strictly on odor.  Odors from the old-age group drove the evaluator’s ability to discern age.  The researcher also said that they found that the young evaluators rated the old-age body odors as being less intense and not as unpleasant as the odors from the young and middle-age groups.

“Elderly people have a discernible underarm odor that younger people consider to be fairly neutral and not very unpleasant,” said Lundström. “This was surprising given the popular conception of old age odor as disagreeable. However, it is possible that other sources of body odors, such as skin or breath, may have different qualities.”

In future studies, the researchers will try to identify the primary biomarkers that evaluators use to identify age-related odors and to determine how the brain is able to identify and measure this information.