Acanthosis nigricans is a skin disorder in which there is darker, thick, velvety skin in body folds and creases.
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 insulin resistance.
Some medicines, particularly hormones such as human growth hormone or birth control pills, 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.
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, your doctor may order tests. This may include:
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.
Call your health care provider if you develop areas of thick, dark, velvety skin.
Habif TP. Cutaneous manifestations of internal disease. In: Habif TP, ed. Clinical Dermatology. 5th ed. Philadelphia, Pa: Mosby Elsevier;2009:chap 26.
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.