Definition of Acanthosis nigricans:

Acanthosis nigricans is a skin disorder in which there is darker, thick, velvety skin in body folds and creases.

Causes, incidence, and risk factors:

Acanthosis nigricans can affect otherwise healthy people, or it can be related to medical problems. Some cases are genetically inherited. The condition is most commonly seen among people of African descent, in part because it is easier to see in darker skin.

Obesity can lead to acanthosis nigricans, as can some endocrine disorders. It is often found in people with obesity-related 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.