"Acanthosis nigricans is a brown to black, poorly defined, velvety hyperpigmentation of the skin. It is usually found in body folds,[1] such as the posterior and lateral folds of the neck, the axilla, groin, umbilicus, forehead, and other areas."
Basically if you have it, you'll know.
Usually, A.N. has a medical cause, but they've never found a reason for mine. Just wondering if any other alopecians have this...I'd love to be able to figure out this "mystery condition" of mine.