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.
Acanthosis nigricans 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. These symptoms are more common in people with cancer.
Signs and tests
Your health care provider can usually diagnose acanthosis nigricans by looking at your skin. A skin biopsy may be needed in unusual cases.
If there is no clear cause of acanthosis nigricans, you may need to have tests. Your health care provider may order blood tests, an endoscopy, or x-rays to rule out diabetes or cancer as the cause.
Because acanthosis nigricans usually only changes the skin's appearance, no treatment is needed.
It is important, however, to treat any underlying medical problem that may be causing these skin changes. When acanthosis nigricans is related to obesity, losing weight often improves the condition.
Acanthosis nigricans often fades if the cause can be found and treated.
Calling your health care provider
Call your health care provider if you develop areas of thick, dark, velvety skin.
Morelli JG. Diseases of the epidermis. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap. 656.
Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine; and Roy Colven, MD, Dermatologist, Associate Professor of Medicine, University of Washington Medical School, Seattle, Washington. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.