Pityriasis versicolor (Tinea veriscolor) is a fungal infection caused by commensal yeasts in hot and humid conditions. They may be reddish brown, slightly scaly patches or ugly, depigmented areas that will not tan, especially in suntanned skin.
Selenium sulphide lotion can be applied for around 10-15 minutes, rinsed off and re-applied daily for about a week. It is less messy and preferably easy to use than the Selsun and Ketoconazole shampoos which needs to applied on the patches of affected skin after an evening bath, left to dry the whole night and washed off the next morning. Please remember that the patches will take a long time to disappear and the treatment does not equate with disappearance.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.