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.

There is no single best medicine, as the right treatment depends entirely on where the infection is and what type of fungus is causing it. For common skin infections like athlete's foot or ringworm, topical creams containing clotrimazole, miconazole, or terbinafine are highly effective. For nail infections or more stubborn cases, oral medications like fluconazole or terbinafine are typically used. Because using the wrong treatment can delay healing, I highly recommend consulting a healthcare provider. They can properly examine the area and prescribe the exact medication you need to clear it up safely.