What are the symptoms for Acanthosis nigricans?

Skin changes are the only signs of acanthosis nigricans. You'll notice dark, thickened, velvety skin in body folds and creases — typically in your armpits, groin and back of the neck. The skin changes usually appear slowly. The affected skin may also have an odor or itch.

When to see a doctor

Consult your doctor if you notice changes in your skin — especially if the changes appear suddenly. You may have an underlying condition that needs treatment.

Source: http://www.mayoclinic.com