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Scientists have completed an usual survey. It's a census, the first of its kind, of the fungi that live on our skin. As NPR's Rob Stein reports, the survey is part of an effort by scientists to better understand the microbes that inhabit the human body.

ROB STEIN, BYLINE: Trillions of microbes can be found pretty much everywhere on our bodies. Bacteria, viruses, most are harmless and many are actually helpful. But Julie Segre, of the National Institutes of Health, says scientists are just starting to figure out exactly what they are and what they do.

JULIA SEGRE: A lot of medicine has to do with not just our own human cells but really about how humans interact with the bacteria and fungi that live on our bodies.

STEIN: Scientists have learned a lot about the bacteria that live in our digestive systems and other places but fungi, like yeast and other molds, have remained a mystery.

SEGRE: So we did an exploration where we looked at all the different little crevices of your body, the sides of your nose, behind your ears.

STEIN: Inside the elbow, on our backs - all together, the researchers sampled 14 spots on 10 healthy adults and used sophisticated genetic technique to see which funguses were living where. In this week's issue of the journal Nature, they report some surprising results.

SEGRE: What we found was that the human body is an even more diverse ecosystem than we had known when we looked only at the bacterial communities.

STEIN: Dozens of different types of fungi are thriving on our bodies, way more than anyone knew, especially in one place.

SEGRE: The feet.

STEIN: The feet were just teeming with fungi.

SEGRE: We found tremendous diversity of fungi on the feet of these healthy volunteers. On the heel, we could find at least 80 different types of fungi. On the toe, at least 60 different types of fungi when most of the body sites only had between two and five different types of fungi.

STEIN: Scientists aren't sure why that is. It could be something about how our feet go hot and cold so much or it could be something much simpler.

SEGRE: Even those of us who wear shoes a lot still walk around barefoot, either in our homes or in locker rooms. And there's just great exposure to fungi.

STEIN: Whatever the explanation, the survey could lead to new ways to treat millions of people who suffer from all sorts of conditions, conditions caused when fungi run amuck, like toenail infections and athlete's foot.

SEGRE: It really would certainly underlie the idea that you really do need to take very good care of your feet. So, for example, I do wear flip-flops when I walk around a locker room because I know from these studies that I don't actually want to share the fungi with the, you know, 20 other people who are showering after just going swimming.

STEIN: The researchers had another surprise. In one volunteer who had taken an antifungal drug, the normal healthy fungi were still out of whack seven months later.

SEGRE: Oh, that was very surprising to us. We tend to think that there is this resilience of our bacterial communities, of our fungal communities, and that as soon as we stop medicating that they would bounce back into a state of health.

STEIN: But this says maybe not and that all the antibiotics, antibacterial products and antifungals that we use these days may be disrupting the good microbes in and on our bodies more than we think. Martin Blaser's a microbiologist at New York University.

MARTIN BLASER: The scale at which people are being exposed to antimicrobial drugs is really substantial. And it would be surprising if there were no consequences from that.

STEIN: The new survey could help shed light on those consequences and other questions, like why women get yeast infections when they take antibiotics, why some people get dandruff and some babies get diaper rash and others don't, and even perhaps how to prevent skin cancer. Rob Stein, NPR News.

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