Acanthosis nigricans (AN)
is a skin disorder in which there is darker, thick, velvety skin in body folds and creases. This condition usually appears slowly and doesn't cause any symptoms other than skin changes. Eventually, dark, velvety skin with very visible markings and creases appears in the armpits, groin and neck folds, and over the joints of the fingers and toes. Less commonly, the lips, palms, soles of the feet, or other areas may be affected. The exact cause of this condition is not well understood; but it can be inherited or related to medical problems such as obesity, diabetes mellitus (insulin- resistance), some prescription drugs, and cancer. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.