For the gender that considers itself the more fastidious (and has the studies to back up the claim), women might be chagrined to learn that they harbor more varieties of germs on their hands than men do.
In fact, we all – male and female – have whole worlds on our hands, and they’re more diverse than anyone suspected.
In a study published online last week in the Proceedings of the National Academy of Science, researchers at the University of Colorado, Boulder, swabbed 102 human palms and found more than 4,700 species of bacteria.
Species varied from person to person; just five were shared among all 51 of the study’s student volunteers. They even differed from hand to hand. An individual’s right had different species from the left.
It’s well-established that hands are hotbeds for bacteria, hence the guidance offered by the national Centers for Disease Control and Prevention to wash them frequently.
What set this study apart is that it looked not at abundance but at diversity.
It did so by extracting DNA from samples gathered on cotton swabs rather than using the standard method of trying to culture the samples in Petri dishes to see what kinds of bacteria would grow.
“Bacteria are tough to identify,” said Noah Fierer, assistant professor of ecology and evolutionary biology and the paper’s lead author. “Most of them can’t be grown in the lab. The best way we have of identifying them is to look for their DNA.”
Fierer doesn’t know why women’s hands have roughly 40 percent more species of bacteria. It could be that men’s more acidic skin discourages some species, or that sweat, hormones or women’s greater use of hand creams play a role.
“The findings don’t necessarily mean that women have more germs than men, just more variety,” he said in a phone interview.
Not all bacteria found on hands are harmful.
Most are probably neutral, Fierer said, and some might protect the skin from pathogenic varieties.
Washing hands, by the way, reduces the abundance but not the variety of microbes, the study found.