Men's offices harbor significantly more bacteria than women's, according to a new study published in the online journal PLoS ONE.

The types of bacteria are the same, and come mostly from the skin, nose, mouth and digestive tract.  Several types are also commonly found in feces.

Researchers from the San Diego State University and the University of Arizona took 450 samples from different office surfaces in New York City, San Francisco and Tucson, Ariz.

Chairs and phones had the highest amount of bacteria, while desktops, keyboards and computer mice had fewer bacteria.

One of the main reasons the researchers did the study was to learn more about what microorganisms inhabit workplaces.

"Westerners spend about 90 percent of time indoors in artificial environments that we build, and workplaces are where we spend a lot of our time," said co-author Scott Kelley, a professor of biology at San Diego State.

Kelly said he believes men's work spaces have more bacteria simply because men are generally bigger than women, though there could also be other reasons.

For example, he said, "Skin is a major source of the bacteria, and if men's hands are physically bigger, there's more surface area to colonize bacteria.  Men's mouths are also bigger."

Philip Tierno, a clinical professor microbiology and pathology at NYU Langone Medical Center, said another reason is that men just aren't as clean as women.

"Men tend to be less tidy.  They wash their hands less than women and tend to be a little more cavalier about eating from the floor or from other surfaces," he said.  Tierno was not involved in the study.  "Also, numerous people touch chairs and phones, but not as many people touch keyboards."

Previous research found that the opposite is true - women's offices are more contaminated than men's, perhaps in part because women use cosmetics and are more likely to store food in their desks.

Kelley explained that one reason for the discrepancy is because both studies looked at different office surfaces.

In addition to differences between men and women, Kelley said the study also found that there was no significant difference between the types of bacteria found in offices in San Francisco and New York. In Tucson, though, there were different types of bacteria associated with drier, desert-like climates.

Though there may be a lot of bacteria in office spaces, Kelley said, most of it doesn't do much harm.

"Most of what's brought in is harmless, but it's very easy to spread.  If someone gets sick, they should stay home because they are bring bacteria in with them and making others sick."