The Fungus Amungus

There was a recent study published in Nature that looked at all the fungi that live on human skin. What was different about this study is that they used DNA to identify the different species, and found a lot more than can usually be found by culturing. The study found a huge profusion of fungi on our feet.

What do you mean “we”, paleface?

Here’s a quickie explanation of the study, Foot Fungus Revealed: A new study profiles the garden of fungal organism that grows on human feet.

Athlete’s foot and toenail fungus are just the tip of a fungal iceberg when it comes to the species that inhabit the human foot, according to a recently published study. Researchers at the National Institutes of Health found an average of 50 species of fungi living on the feet of 10 healthy adults.

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The scientists also swabbed the study participants’ other body parts—including behind the ear, between the eyebrows, and on the chest, back, nostril, scalp, and various parts of the arm. But nowhere were fungal communities more diverse than on the foot.

The study itself, Topographic diversity of fungal and bacterial communities in human skin, looked for both fungi and bacteria at all sorts of different places on human skin, using DNA markers to do so. (More precisely, they prepared DNA, amplified it, and sequenced two phylogenetic markers within the 18SrRNA ribosomal RNA region.)

The people they tested were 10 healthy adults from the Washington, DC area. For a week before the test, they were not allowed to bathe or shower with an anti-bacterial soap (regular soaps were okay). And they weren’t allowed to bathe at all for the day before the test.

There were a huge number of sites tested, from the middle of the upper back, to the crease behind the ear, to the inner forearm, to the palm, to three spots on the feet (plantar heel, toenail, toe web).

Here’s their money picture.

Figure 1 | Relative abundance of fungal genera and Malassezia species at different human skin sites.

The way to look at that is to realize that across the top it’s labeled 1 through 10. Those are the results for each of the 10 subjects. (In case you’re curious, Subject #7 had been on an anti-fungal medication 7 months previously. It looks to me as if the anti-fungal killed off his entire fungal microbiome, including the symbiotic protective ones, allowing his body to be colonized by a huge number of different ones once the anti-fungal was stopped.)

Along the side they show the different body locations. The last 3 locations are the ones on the feet. You can see the vast profusion of species there.

But also note the location just above those three, the hypothenar palm (area closest to the little finger).

Now, if you think about it, our hands and feet are really quite similar. Same kinds of digits, no hair on the bottoms. Genetically, they are built in much the same way, with just a few (relatively-speaking) regulating genes creating the differences.

So, why would there be such a huge difference in the colonization by fungi between hands and feet?

Anybody care to hazard a guess? (Trick question.)

Of course, these people are all from Washington. Of course they are constant shoe-wearers. This is what happens when you enclose a body part in a dark, warm, moist environment with poor air circulation for long periods of time.

If they’d made everybody constantly wear gloves for a month before the test I bet there’d be similar results on the hands.

The sad thing is, this study just reinforces the idea in people’s minds that there is something wrong with feet. Ewww, see how icky they are! We have to ban bare feet.

But what the study really shows is that there is something wrong with shoes.