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 looking at the appearance of 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.