Acanthosis nigricans, also known as Dark neck black neck, is a skin condition that causes darker, thicker skin and that may feel velvety. It usually appears on the neck, folds of the Glutathione Assist Capsules Advance Glutathione Tablets Dr. Kasana's Clinic Acanthosis nigricans is a medical sign characterised by brown to black, poorly defined, velvety hyperpigmentation of the skin. It can also be due to some underlying disease, so don't ignore & consult your doctor. . . #