This sounds like tinea cruris, commonly known as jock itch, which is a highly treatable fungal infection. You can use over-the-counter antifungal creams containing generic active ingredients such as clotrimazole, miconazole, or terbinafine. Apply a thin layer to the clean, dry affected area twice daily, extending slightly beyond the edge of the rash. Continue treatment for one to two weeks after your symptoms disappear to prevent them from returning. Keep the area clean and dry, and wear loose-fitting cotton clothing. If the rash does not improve after two weeks, please consult a doctor for further evaluation.