Someone mentioned that you usually contract athlete's foot in gyms and saunas? Not in my experience. I haven't been in a gym or a sauna in years, but have gotten a mild case of athlete's foot now and then on a reasonably frequent basis, so I think it's just ordinary footwear that does it.

My GP (recently retired) told me that he'd seen far more, and worse, fungal infections in people who wore trainers than those who wore more old-fashioned types of shoe. I suspect the people who claim you catch these infections from going barefoot in the gym have got it exactly wrong: people who go to the gym are likely to spend more time than others with their feet in sneakers, with their feet getting hotter and sweatier than the average.

I've been wearing sandals without socks most of the year for years, and I now get far less fungal infections than I used to when I covered my feet more. The organisms that cause tinea are ubiquitous, you can't expect to prevent exposure. But you can avoid turning your feet into a culture medium.