Hello and welcome to healthcaremagic I would keep a possibility of fungal infection/tinea pedis. This is because closely opposing body folds e.g finger webs, thighs and groin, axilla, submammary folds etc can trap sweat, heat and moisture, therefore making the area favorable for fungal proliferation. The black powder like thing that comes off on scratching is actually dead skin/ epidermis. If I was the treating doctor I would have asked you to use a topical antifungal like clotrimazole/sertaconazole/luliconazole cream, twice daily, regularly for 4 weeks. Etaze AF cream contains topical terbinafine+mometasone. I would rather prefer a plain antifungal like clotrimazole/sertaconazole/luliconazole because mometasone if used for too long can cause side effects like skin atrophy and striae Since you are already using an Oral antifungal e.g oral terbinafine once daily. I would suggest you to continue with it for 4-6 weeks for a more complete cure An OTC antihistamine e.g cetrizine 10mg once daily would help you in symptomatic itch relief. Keeping the folds dry by using an antifungal dusting powder would help in preventing the recurrence. regards