Most feet are encased in shoes for 12 hours or more per day, providing the perfect warm environment for fungus. If you work out, this situation is exacerbated as sweat creates an even more optimal environment for foot fungus: a dark, moist shoe, and communal areas such as the locker room or showers, to spread the condition. Moccasin foot is a fungal infection, which first just appears to be dry skin. The sole of the foot is covered in a dusty, scaly material on top of a reddish background, giving the appearance that you are wearing slippers, or moccasins.
Apply anti-fungal spray to the entirety of your foot for one to two weeks, focusing on the soles.
Spray or powder the interior of your shoes with an anti-fungal treatment designed for footwear. This is crucial, as you don't want to simply reinfect your feet once they've healed, if the fungus is still living in your shoes.
Swab the sole of the foot daily with a clean cotton ball and some surgical spirit. Surgical spirit is a methylated spirit with trace quantities of wintergreen and castor oil. This helps the foot heal, and is also a preventive measure.
Change your socks regularly. Make sure your feet are properly dried after each shower or bath.
If the problem persists, see your doctor.