Symptoms:

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.