If one of your concerns about getting older is that you'll have that so-called ''old people's smell" that is the butt of jokes and bad birthday greeting cards, here's some new, reassuring research.

Older people "do have a characteristic odor, but it's not a negative odor," says Johan Lundstrom, PhD, a sensory neuroscientist at the Monell Chemical Senses Center, a research institute in Philadelphia.

"The negative association with old people's body odor seems to come from our negative association with old age," he tells WebMD.

In his new research, middle-aged men actually were evaluated as most stinky of three adult age groups. Middle-aged women smelled best.

The study is published in PLoS ONE.

Smell of Age: Research

In previous animal studies, Lundstrom tells WebMD, researchers have found that body odors carry age-related information. Animals can detect and process that information.

Doing so helps them with such tasks as picking suitable mates for reproducing.

In people, a unique "old person's smell" has long been talked about. In Japan, they have a special word for it -- kareishu.

As a child, Lundstrom says he sometimes visited his mother at her job as head nurse at a retirement community. Years later, he gave a talk at a retirement home.

"The odor hit me," he says. It was the same odor he had smelled as a young boy in Sweden, he says.

Lundstrom wanted to see if the animal odor findings might also hold true with people.

Sniffing Out Age: Study Details

For the study, Lundstrom first collected body odor from three age groups: 20 to 30, 45 to 55, and 75 to 95. Each group had 12 to 16 men and women.

Each person slept in an unscented T-shirt with underarm pads for five nights.

Next, they gave the pads to Lundstrom. He cut each pad into four pieces and put them in glass jars.

Next, 41 young evaluators, all aged 20 to 30, were given the jars with the pads. They were asked to identify which came from which age donor.

They also asked how intense they found the odor on the pads and how unpleasant.

Sniffing Out Age: Results

''The majority could categorize old body odor as old," Lundstrom tells WebMD. They were not as good at picking out the odor of younger people, he says.

"There is something with the body odor that is helping to associate age," he says.

Experts know that body odor changes with age.

However, the evaluators did not rate the old people's odor as unpleasant.

They did find the odor of middle-aged men particularly unpleasant. "The worst-smellers are middle-aged men," Lundstrom says. "The ones who smelled the most beautiful are middle-aged women."

Form best to worst smelling, here is how the people stacked up:

• Middle-aged women
• Old men
• Young women
• Old women
• Young men
• Middle-aged men -- who lagged way behind other categories, Lundstrom says.

'Old Person's Smell': Perspective

The study confirms there is an ''old person's smell," says Jane Mohler, PhD, MPH, associate director of the Arizona Center on Aging, University of Arizona. She reviewed the findings for WebMD.

"But it also says the older person's smell was less intense and less unpleasant [than some other ages]," she says.

The odor associated with some older people, Mohler says, could have more to do with hygiene or diet habits or illness than physiology.

"We all know how sweet babies smell when they are clean," she says. And, she adds, we know how badly they can smell before a bath or a diaper change.

"Body odor changes [with age]," she says. "But body odor does not have to be bad as we age."

How to Age Fragrantly

For people getting older and fearing ''old person's smell," Lundstrom says don't worry.

"As long as one showers when one should shower and you air out your abode [where body odors can accumulate], you are good to go," he says.

SOURCES: Johan Lundstrom, PhD, sensory neuroscientist, Monell Chemical Senses Center, Philadelphia.Jane Mohler, PhD, MPH, associate director, Arizona Center on Aging, University of Arizona, Tucson.Mitro, S. PLoS ONE, May 2012.

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