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

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 cancers of the gastrointestinal or genitourinary tracts or with lymphoma 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. Sometimes, the lips, palms, soles of feet, or other areas may be affected.

Your physician can usually diagnosis acanthosis nigricans by simply looking at your skin. A skin biopsy may be needed in unusual cases.

If no clear cause of acanthosis nigricans is obvious, it may be necessary to search for one. Your physician may order blood tests, endoscopy, or x-ray studies to eliminate the possibility of underlying diabetes or cancer.

Because acanthosis nigricans itself usually only causes changes to the appearance of the skin, no particular treatment is needed.

It is important, however, to attempt to treat any underlying medical problem that may be causing these skin changes.

Acanthosis nigricans often fades if the cause can be found and treated.

Call your physician if you develop areas of thick, dark, velvety skin.