Most people will tell you that you're probably safe if you don't wear shower shoes at the gym, but it's not a chance you should be willing to take. Warm, moist environments like your gym's shower stalls are the places where fungi thrive, and if your feet are not protected by shower shoes, it's easy to pick one up. Going into shower stalls unprotected can lead to athlete's foot or even onychomycosis [1], an infection that turns toenails hard and yellow, says Jane Andersen, a podiatrist and a spokesperson for the American Podiatric Medical Association.

Both infections can require over-the-counter and prescription antifungal treatments, and if you pick up onychomycosis at the gym, it can be a lengthy process that takes months to fully treat. If you're blessed with a painful plantar wart [2] that doesn't clear up with over-the-counter treatment, you can plan at least one uncomfortable (and, in some cases, expensive) trip to your dermatologist's office.

While none of these ailments is life threatening, they can prove to be painful — or just a pain in general. As long as you keep your feet dry, wear clean socks at the gym, and don't share shoes, you can easily prevent these foot problems by simply slipping on some shower shoes. In short, we're sold: rubber flip-flops are well worth the $2 investment.