Look for symptoms of acanthosis nigricans, a skin condition commonly caused by elevated levels of insulin. Excess insulin causes skin cells to multiply and creates too much melanin, resulting in dark, velvety patches of thicker skin in body folds and creases. These areas are most commonly found around the neck, armpits and groin area. There is no burning or itching associated with acanthosis nigricans, which can lead people to believe darkening skin is normal. While there are some creams available that can thin the thickened skin, it is crucial to see a doctor as the changes in your skin could be indicative of type 2 diabetes.