Hello, It may be acanthosis nigricans, a skin condition that is seen in obese and diabetic patients. It will be velvetty on feeling with your fingers. Increased insulin is supposed to cause the problem. So, only topical skin whitening cream won t work. I prescribe Tab. Metformin, Topical retinoids for this. Need to consult a diabetologist for control of blood sugar, and he may also refer to ophthalmologist to rule out diabetic retnopathy. If you feel the your condition is different from this description, feel free to send clinical image. Hope I have answered your query. Have a nice day.