Are you overweight? Or has your weight increased of late? Do you constantly eat unhealthy foods, sleep late and do not exercise? If the answer to any of the above is yes then you (based on your description of pigmentation ) most likely have Pseudoacanthosis Nigricans . This happens because of Insulin resistance in people who lead unhealthy lifestyle . The best treatment is to start MODIFYING LIFESTYLE . But you will have to visit a dermatologist allopathic near you to confirm what I said. That dermatologist will explain in detail.