A skin condition charac- terized by dark, thickened, velvety patches, espe- cially in the folds of skin in the armpit, groin, and back of the neck. It can occur with endocrine dis- eases such as Cushing disease and diabetes mellitus, from tumors of the pituitary gland, underlying malig- nancies, certain drugs, and as a genetic disorder. It is most common in people who have insulin resist- ance—those whose body is not responding cor- rectly to the insulin that they make in their pancreas.