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What is acanthosis nigricans?Acanthosis nigricans (AN) is a skin disorder characterised by darkening (hyperpigmentation) and thickening (hyperkeratosis) of the skin, occurring mainly in the folds of the skin in the armpit (axilla), groin and back of the neck.Acanthosis nigricans is not a skin disease per se but a cutaneous sign of an underlying condition or disease.There are two important types of acanthosis: benign and malignant. Although classically described as a sign of internal malignancy, this is very rare. Benign types, sometimes described as ‘pseudoacanthosis nigricans’ are much more common.
FrequencyUnited StatesThe exact incidence of AN is unknown. In an unselected population of 1412 children, the changes of AN were present in 7.1%. Obesity is closely associated with AN, and more than one half of the adults who weigh greater than 200% of their ideal body weight have lesions consistent with AN. The malignant form of AN is far less common, and, in one study, only 2 of 12,000 patients with cancer had signs of AN.