Hello, Usage of certain medications causes hyper-pigmentation in the groin like cortico-steroids, high doses of niacin, etc. In cases of gastric adenocarcinoma, other carcinomas and lymphomas, malignant nigricans can occur with hyper pigmentation. You are suggested to get a complete medical health check up done to detect the pathology causing the symptom so that it can be treated at the earliest. Maintain healthy weight, control blood glucose level at all cost. Take care of your hygiene and get clinically examined to rule out any fungal infection or jock itch. Use antibacterial soaps, topical antibiotics (Bacitracin ointment). Get connected to a dermatologist, you can apply locally prescription creams (Hydroquinone) to lighten skin but laser treatments are still better and more effective. The dermatologist will tell you to do a skin biopsy to detect if it is malignant so that the treatment can be started. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Nupur K., General & Family Physician