Athlete's foot isn't just an irksome itch; it's a fungal infection that can turn your skin scaly. Fungi can also invade your nails, making them yellow and chalky. Either condition can progress to a more severe infection, says dermatologist Evan Rieder, M.D., of NYU School of Medicine.

Attack Plan

Foot fungus can be notoriously hard to treat because it can return and spread; you're better off preventing it. Fungi befriend your feet in warm, moist environments, like sweaty shoes, so sprinkle some Zeasorb Athlete's Foot, a powder with the antifungal miconazole nitrate, into your shoes and on your feet before workouts, Dr. Rieder says. If you're already infected, don't mess around. Ask your doctor for a prescription antifungal product.