Hi, I can understand your concern for skin on thighs between legs turned to black in color and peeling. You have not told us your relevant details like your age, sex and occupation. After reading your query it appears to be due to Fungal infection of the thigh area which is quite common due to heat and humidity. Fungal infection of the skin is quite common due to infection and hygiene as well as most commonly due to diabetes. Go for your blood sugar check up to rule out diabetes and raised blood sugar if you are more than 40 years of age. To prevent the further spread maintain good hygiene wash it two times properly. Stay away from hot and humid climate. You can use clotrimazole cream or terbinafine cream over the affected areas under medical supervision. I suggest you to take antifungal tablet by mouth such as fluconazole 150 mg alternate days for 15 days. Take care.