I think what it comes down to is letting the parent know when enough is enough and that what is being done at the moment is no longer working and it is time for a new course of action. That could mean saying ok the creams we are using now are no longer effective and it is time for something stronger or to rule out the need for something specialized such as due to an infection. That obviously means a trip to the doctor. I do like to remind parents who see this request as a need for time off that an evening walk in clinic is quite capable of diagnosing a diaper rash and prescribing the required ointments.