If you notice dark brown or whitish circles on your skin, particularly on your chest or back, you probably have a fungus infection called tinea versicolor.
Tinea versicolor is especially noticeable as white spots on your skin when you try to get a suntan.
You don’t have to treat it as it usually causes no harm and does not itch, but it is highly contagious. The fungus produces a chemical that takes pigment out of the skin to cause the circular color changes. You usually don’t notice it during the winter, but when you go out in the sun, the circles appear because you tan everywhere but where the fungus lives.
You can cure it just by three days of applying non-prescription Selsun blue shampoo from your neck to your waist to your wrists, leaving it on for at least 10 minutes and then showering it off, or by taking a 150 mg Diflucan pill once a day for three straight days. However, you will probably get the fungus infection back from your clothes, your mate, towels, pillow cases, sheets and so forth. You can help to prevent reinfection by washing everything, treating your mate at the same time, and applying the Selsun Blue once every couple of weeks for several months.