Dear user, I think you are doing the right thing. Petroleum jelly is an inert, moisturising substance, so regardless of the diagnosis, at least we know that it won t cause more harm. Okay, so the rash seems to be either nappy dermatitis (more likely) or a fungal infection (less likely). On the other hand, it may turn out to be just a different manifestation of what is known as seborrhoeic dermatitis. If the rashes don t change within the next few days, you might want to do one of the following: take him to the doctor for an official consultation, or try an application or two of a mild steroid cream (if you have one) and see the result of the same. If it works out, then the diagnosis of nappy dermatitis or seborrhoeic dermatitis is most likely. - Dr. Taher