Acanthosis nigricans (or AN) is a disease of the skin. It causes the area of affected skin to thicken (hyperkeratosis), and brown spots of varying size (hyperpigmentation) to appear on the entire body, particularly on the body's folds (i.e. elbows, armpits, knees). Acanthosis nigricans may affect men and women equally, but primarily affects those with dark skin and it is very often associated with obesity. Moreover, the majority of people afflicted with acanthosis nigricans also suffer from endocrine disorders and diabetes.