Acanthosis nigricans (pronounced: ah-kan-THO-sis NY-gruh-kans) is a skin condition. It appears gradually with thicker and dark, velvety patches of skin in body creases and folds, usually on the sides and back of the neck, in armpits, elbow pits and groin. It can be found on other parts of the body, including the face, chest, elbows, knees, and knuckles.

Acanthosis nigricans is most commonly caused by high blood insulin levels, a condition called insulin resistance. Insulin resistance is seen in people who are overweight or obese and makes them more likely to develop type 2 diabetes. It is also associated with other endocrine conditions, such as polycystic ovary syndrome (PCOS).

Losing weight will help acanthosis nigricans fade.