Picture of Acanthosis Nigricans
Acanthosis nigricans. Also called Velvety plaques, this is a thickening of the outer layer of skin resulting in a discoloration of brown-to-black. They can develop in the folds of the armpit, groin and/or neck and can start showing up during childhood or adulthood. Seeing this condition suggests diabetes or simply obesity. In rare cases acanthosis nigricans occurring in other places, such the hands or lips, may indicate an internal malignancy.
Text Source: American Academy of Dermatology Association