(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.

A catastrophic event such as increased volcanism may have contributed to massive extinction event (Photo: National Park Service)

More than 250 million years ago, most life on Earth was wiped out by a catastrophic event called the Permian–Triassic extinction. New research suggests it took our planet 10 million years to recover from what is now known as “The Great Dying.”

The Great Dying took place millions of years earlier than the Cretaceous-Tertiary extinction, which killed off the dinosaurs 65 million years ago. It was also much more devastating, destroying 90 percent of all plants and animals.

Scientists theorize a “perfect storm” of conditions – global-warming, acid rain, ocean acidification and ocean anoxia (loss of oxygen) – followed by a catastrophic event such as increased volcanism, contributed to Earth’s most dramatic and devastating biological crisis.

For some time now, they’ve debated how quickly life on Earth bounced back from this mass extinction. A new article in Nature Geoscience puts that number at 10 million years.

Artist rendering of The Great Dying in which 90 percent of all marine species are thought to have perished. (Image: Lunar and Planetary Institute)

So why did it take our planet so long to recover from this devastating loss of life? Why didn’t life just “bounce back?”

The sheer intensity of this crisis, coupled with the bleak conditions which remained on Earth after that first devastating surge of extinction, are the reasons for the delay, according to the report authors.

These bleak conditions continued, in bursts, for some five-to-six million years after the initial calamity, triggering repeated environmental crises.

“Life seemed to be getting back to normal when another crisis hit and set it back again,” said Michael Benton, one of the report authors who is a professor at England’s University of Bristol. “The carbon crises were repeated many times and then, finally, conditions became normal again after five million years or so.”

Map of the world around the time of the Great Dying (Image: Dr. Ron Blakey via Wikimedia Commons)

While certain groups of marine and land animals recovered quickly to a certain point, they suffered continual setbacks with each of these bursts of dire conditions following the initial crisis because, according to the researchers, their permanent ecosystems were not firmly established.

But after the waves of environmental devastation began to wane, not only did life return to Earth, but much more complex ecosystems were formed, allowing for much more sophisticated life forms which eventually led to human life.

“We often see mass extinctions as entirely negative but in this most devastating case, life did recover, after many millions of years, and new groups emerged,” Benton said. “The event had re-set evolution. However, the causes of the killing – global warming, acid rain, ocean acidification – sound eerily familiar to us today. Perhaps we can learn something from these ancient events.”