Overview
Acanthosis nigricans is a condition that causes areas of dark, thick velvety skin in body folds and creases. It typically affects the armpits, groin and neck.
Acanthosis nigricans (ak-an-THOE-sis NIE-grih-kuns) tends to affect people with obesity. Rarely, the skin condition can be a sign of cancer in an internal organ, such as the stomach or liver.
Treating the cause of acanthosis nigricans might restore the usual color and texture of the skin.

Acanthosis Nigricans
Acanthosis nigricans is a skin condition that causes a dark discoloration in body folds and creases. It typically affects the armpits, groin and neck.
Symptoms
The main sign of acanthosis nigricans is dark, thick, velvety skin in body folds and creases. It often appears in the armpits, groin and back of the neck. It develops slowly. The affected skin might be itchy, have an odor and develop skin tags.
When to see a doctor
Consult your health care provider if you notice changes in your skin — especially if the changes are sudden. You may have an underlying condition that needs treatment.