Hello,
These patches can be due to pityriasis versicolor. 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. Melasma is caused by hormonal changes, which stimulate a temporary increase in your body's production of melanin. People with darker complexions are more prone to this condition than people with lighter skin.
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.
More like a sun induced photo-reaction from what is seen here.