Definition of Acanthosis nigricans:

Acanthosis nigricans is a skin disorder characterized by dark, thick, velvety skin in body folds and creases.

Causes, incidence, and risk factors:

Acanthosis nigricans can affect otherwise healthy people, or it can be associated with medical problems. Some cases are genetically inherited. It is most common among people of African descent.

Obesity can lead to acanthosis nigricans, as can many endocrine disorders. It is frequently found in people with diabetes.

Some drugs, particularly hormones such as human growth hormone or oral contraceptives ("the pill"), can also cause acanthosis nigricans.

People with lymphoma or cancers of the gastrointestinal or genitourinary tracts can also develop severe cases of acanthosis nigricans.