Published: March 1, 2009

Next time you shake your female colleague’s hand, you may want to visit the washroom.

Women carry a greater variety of bacteria on their hands than men, according to a CU study that took samples from 51 college students. Using a new, highly detailed system for detecting bacteria, the researchers found more types of bacteria than expected on everyone’s hands — with about 150 different species living on a typical hand.

“I view humans as ‘continents’ of microscopic ecological zones with the kind of diversity comparable to deep oceans or tropical jungles,” says professor and lead study author Noah Fierer of ecology and evolutionary biology. “Today we have the ability to answer large-scale questions about these complex microbial communities and their implications for human health that we weren’t even asking six months or a year ago.”

The greater bacterial diversity found on women’s hands may be attributed to skin pH, as men tend to have more acidic skin and research indicates there are fewer microbes in acidic environments. Hormones, moisturizers, sweat and oil production also could play a role, Fierer says.

The researchers hope the results will help establish a healthy baseline to detect microbial community differences on individuals that are associated with a variety of human diseases. While the researchers stressed regular hand washing has a positive effect, they noted the vast majority of bacteria are nonpathnogenic and some bacteria actually aid in preventing the spread of pathogens.