hello and welcome to HCM
could you please clarify how large the lesions are and where precisely they are located i.e upper back or lower. you mentioned living in a humid climate, do you sweat a lot? do you have oily skin? does any one else in your immediate surroundings have these lesions. i would advise you to have a basic blood test
done and visit a dermatologist
this condition you are having might be a simple fungal infection(tinea versicolor
). allergies to drugs or food usually cause a fixed lesion that appears and goes over time.