John:
Most likely, you have a mild fungus clled tinea versicolor. It's not contagious, and quite common. Try OTC clotrimazole 1% cream from your drugstore, twice a day for 10 days. If that doesn't do it, I suggest you see a doctor.
This condition often recurs, bu the next time you get it, you'll recognize it yourself.
Best.
Dr. Rockoff