It's not clear why feet are special, Segre said. "But it probably has to do with temperature and the exposures our feet have," she explained.
"The feet are unusual," Relman noted. That, he said, is because other than your hands, your feet have the most contact with the outside world; but when they're not touching your surroundings, they are stuffed inside socks and shoes.
"They're enclosed in this tight container called the shoe," Relman said. "And it gets hot and humid in there, which are the conditions that fungi like."
He said it would be interesting to study other cultures where people keep their feet free of heavy shoes, to see if there's any difference in foot fungal diversity.
And what is the significance of this community diversity? It's not clear.
There was one volunteer in the study whose feet had a particularly broad range of fungal types. And that person had been treated for a toenail infection seven months before the study, with a two-month course of oral antifungal medication.
The researchers don't know if that volunteer had the wide variety of fungal residents first, and that somehow led to the toenail infection. If so, that would be the opposite of what's seen with bacteria, Relman noted.
"From other studies, we know that low diversity [in bacteria] seems to be a risk factor for infections," he said.
Another possibility, according to Relman, is that using antifungal medication opened up real estate for a wider range of fungi to gain a foothold. He said future studies need to look at whether overuse of antifungals -- particularly the topical ones available over-the-counter -- spells trouble for the natural fungal makeup of your skin.
It's already known that improper use of antibiotics, which kill bacteria,
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