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Checkup: Hand Bacteria

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Air date: December 21, 2008


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Scientists have recently discovered that there are more than 4700 types of bacteria living on the human hand. What does this mean? Jeremy Shere explains in this week's Sound Medicine Checkup.

If you were able to look at your hands under a powerful microscope, what youíd see is bacteria. Many different types of bacteria in multiple colors, shapes and sizes.

Is this a problem? To find out, I talked to a hand bacteria expert Rob Knight, an assistant prof of chemistry and biochem at the University of Colorado at Boulder.

Rob did a study to find out how many different kinds of bacteria we have on our hands. And what he found was pretty astonishing. A given human hand is host to nearly 150 different bacteria species. Among all the hands that Rob looked at, he found nearly 5000 kinds of bacteria. He even found that womenís hand bacteria differs from men's.

"Basically what we found is that in the women that we looked at there were more kinds of bacteria on each of the hand surfaces on average in the women than there were in the men. So what this means is not that womenís hands are dirtier in any way -- just that they have more kinds of bacteria on them."

That may be because the skin of mensí hands tends to be acidic than womenís -- making it less attractive for bacteria.

But anyway, should we be worried about all this bacteria?
"Well, we donít know yet, but probably itís not a problem."

That may not sound very reassuring. But consider, Rob says, that the Colorado undergraduates whose hands he studied were all basically healthy. So the bacteria donít seem to be causing any particular harm.

The real lesson here, Rob says, is that bacteria are everywhere. Theyíre part of our bodies, so the more we know about the microbes in and on us, the better we understand what makes us tick.

Iím Jeremy Shere.

This Sound Medicine Checkup is underwritten by IUPUI, where impact is made on our students, our community, our health and our economy. More information at