My nephew, now an adult has a dark crease line in the back of his neck. It really bothers me because it looks like he has a necklace on from behind but I doesn't. It almost looks like a tan right in the crease of the backof his neck which I believe got there when started to gain weight. Maybe it is the way he holds his neck that it has created this line but why has it got dark? What can he do to remove the darkness. He has tried scrubbing extra in that area but only has improved a little. Is this accumulated dirt? Help is there anything he can apply to help that go away?

He has a condition called Acanthosis Nigricans. Sometimes it can mean a person is developing diabetes, but most often, it is a hereditary skin condition that is benign.

Search the internet and you will find lots of info on it.