Photograph by Lynn Johnson, National Geographic

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Phones are among the most bacteria-rich items in offices (file picture).

Photograph by Lynn Johnson, National Geographic

Men's Offices Have More Bacteria, Study Finds

Your work space might harbor about as many bacteria species as a bathroom, a new study suggests—and they come mainly from your own body.

U.S. offices brim with more than 500 species of bacteria, a new study saysabout the same number found in previous studies of a bathroom and an airplane.

But not all offices are equally populated: Men's spaces were found to harbor more microbe species than women's.

(See more health news.)

In developed countries, millions of people spend about 90 percent of their time indoors—most of them working eight or more hours without going outside, according to the study. (Pictures: "Seven Supergreen U.S. Government Buildings.")

Increasingly, "this is the human habitat, and I think it's important to know what is in our human habitat and where it comes from," said study co-author Scott Kelley, a biologist at San Diego State University.

"Since humans are the main source of the bacteria in offices, we are the ones constantly spreading contamination around our environments," Kelley said.

"Normally this is not a problem. However, in places like hospitals and nursing homes, even harmless bacteria can be a problem."

Kelley and colleagues chose three climatically diverse cities—New York City, San Francisco, and Tucson, Arizona—and took swabs from various office surfaces in 30 offices in each city.

To find out "who and what" was there, the scientists cultured—or grew—the sampled bacteria in the lab, as well as analyzed their DNA, Kelley said.

The team found the bacterial communities of New York and San Francisco were "indistinguishable," mostly because the bacteria come from common species that live on people, Kelley noted.

Microbes regularly fall from skin and settle on office surfaces. "I was a bit surprised how much was out there and how much we were contributing to this environment. It's not just blowing in through dust—we're constantly sort of shedding it," Kelley said.

Tucson had different species from New York and San Francisco, likely due to bacteria species adapted to the desert soils in the region, he said.

Why Men Have More Office Bacteria

The team also found bacteria are most concentrated on phones and chairs.

The phone finding makes sense, since people put their mouths near handsets. But the chair discovery is a bit tougher to explain, Kelley said. It may simply be that the scientists' swabs were better able to pick up microbes on chairs than on other surfaces such as bumpy keyboards.

As for why bacteria accumulate in men's offices, Kelley has two hypotheses.

One is hygiene—men "are commonly perceived to have a more slovenly nature," and past research has shown that men wash their hands and brush their teeth less often than women, according to the study.

More likely, however, is that men are simply bigger, Kelley said. Because men's hands and mouths are larger than those of women, there's more surface area for bacteria to grow, he said.

Overall, unless, say, a cold is spreading around, office bacteria are nothing to fear, Kelley said, adding, "I don't want people to be frightened of their own offices."

The office-bacteria study was published in May in the journal PLoS ONE.