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Women's hands are full

Full of bacteria, that is. They have more types than men do, a study says. No one knows why. Wash? Forget it.

November 08, 2008|Mary Engel | Engel is a Times staff writer.

For the gender that considers itself the more fastidious (and has the studies to back up the claim), women may 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 Monday in the Proceedings of the National Academy of Science, researchers at the University of Colorado at 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 than the left.

Hands have long been recognized as hotbeds for bacteria. That's why everyone from mothers to the national Centers for Disease Control and Prevention admonishes us to wash them.

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% more species of bacteria.

It could be that men's more acidic skin discourages some species or that sweat, hormones or women's more frequent 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, rather gallantly, in a phone interview.

Not all bacteria found on hands are harmful. Most are probably neutral, Fierer said, and some may protect the skin from pathogenic varieties.

Washing hands, by the way, reduces the abundance but not the variety of microbes, the study found.

"We're not saying at all that washing hands is not a good idea," Fierer said. "We know that it reduces abundance and has a large effect on pathogens."


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