Hello and Welcome to ‘Ask A Doctor’ service.
I have reviewed your query and here is my advice. Dry flaky skin over the lower back can be localised icthyosis. It is due to excessive washing of the skin over the buttocks area. Use amylac cream over the lesion if not subsided within 4 days go for steroid
cream along with amylac cream.
Hope I have answered your query. Let me know if I can assist you further.
Dr. Raghuveer Murki