Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. Perhaps he has a fungal infection/tinea cruris. The waist/belt area and inner thighs are favorable sites for the fungus to grow. The rash starts as rings which continue to expand and has a dry/scaly surface. While bathing and maintaining hygiene are important measures I also suggest him to take an oral antifungal e.g. either Terbinafine or Itraconazole. In addition I suggest him to apply a topical antifungal e.g. either Luliconazole cream or Sertaconazole cream. He may also take an oral antihistamine e.g Cetrizine tablet for symptomatic relief from itching. Regards.