This is quite a common presenting condition in our clinic, especially the ladies seeing our lady practitioner.
“Acanthosis nigricans is a medical sign characterised by 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 armpits, groin, navel, forehead and other areas.
It is associated with endocrine dysfunction, especially insulin resistance and hyperinsulinaemia, as seen in diabetes mellitus. This activates the insulin-like growth factor receptors, which leads to proliferation of keratinocytes, fibroblasts and other cells in the skin. Activation of other growth factor receptors such as fibroblast growth factor receptors or epidermal growth factor receptor can also be responsible.[2]”. [source: Wikipedia]
The NHS UK website says,
“Although it's usually harmless, it's best to get any skin changes checked out. In rare cases, it can be a sign of something more serious, such as cancer. A GP can usually tell if it's acanthosis nigricans by looking at your skin. You may need some tests if they're not sure what's causing the patches.”
Image
Vandana Mehta Rai MD DNB, C Balachandran MD, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons