Fungal infection on both inner thighs. itchy w/ dark color. week ago skin clear, started using diaper cream 20% zinc. caused by zinc or alcohol use?

Tinea cruris: It is very unlikely that zinc containing diaper rash cream or alcohol discolored your skin, and you will need an antifungal cream. See your primary care doctor.

The issue: Fungal infections can darken the skin as can repeated scratching/rubbing. Clotrimazole of tolnaftate (OTC) would be better treatment if it is a fungus. Clearing with a skin barrier like zinc oxide cream suggests it is not fungal. If it persists you may need to have it examined.