By Deborah Netburn
May 22, 2013
t's time to face the fungal foot facts: On average, each one of us is currently walking around with 100 types of fungi living on the soles of our feet, in between our toes, and on our toenails, according to a new study.
It may sound gross, but that fungal diversity doesn't have to be a bad thing – especially if healthy fungus populations can keep bad fungi at bay, like the kind that causes Athlete's foot or toenail scaling.
“Skin bacteria and fungi have gotten a bum rap,” said Julie Segre, a geneticist at the Human Genome Research Institute and the lead author of the study, published Wednesday in the journal Nature. “But one of the major functions of healthy fungi is to prevent pathogenic fungi from adhering to our skin.”
The research adds another layer to scientists' understanding of the community of bacteria, fungi, viruses, and mites living on and in us and that makes up the human microbiome.
Previous studies on the microbiome of the skin have focused mostly on identifying the different types of bacteria that live on our body surfaces. But in this study, the scientists wanted to learn more about the fungi that call us home.
Ten healthy volunteers agreed to be swabbed for the study – letting Segre's co-author, dermatologist Heidi Kong, take samples from their scalp, nostrils, heels, forearms and the webbing between the toes, among other body parts. She also cut their toenails.
Kong gave the samples to Segre, who used detergents and tiny stainless steel balls to break down the thick fungi cell walls and release their DNA. Then she put each sample through a DNA sequencing instrument to find out what was living where.
The scientists learned that while our foot may be a bacteria desert, it is a fungal wonderland.
The scientists found more than 80 types of fungi thriving on just the heel alone, 60 types in between the toes, and 40 types on the toenails.
On the forehead, for example, they found between two and 10 types of fungi.
The researchers also found that the fungi population on the feet is in constant flux. When volunteers came back for further swabbing after a month or two, only 30% to 40% of the fungi on the feet remained the same.
More research will need to be done to determine why fungi are so fond of feet, and why the population is so vast and unstable, but Segre thinks it may have to do with the extreme temperature changes our feet go through compared with other parts of our body, and obviously, the amount of contact our feet have with the ground.
The research may have implications for treating fungal foot diseases, but Segre also thinks it has implications for how we take care of our feet.
“Our feet are exposed to a tremendous amount of fungi, and when you walk around barefoot, you are sharing your fungi with everyone else in the room,” she said. “This study suggests you should always wear your flip flops in the gym locker room.”