<unk>  is a brown to black, poorly defined, velvety hyperpigmentation of the skin, usually present in the posterior and lateral folds of the neck, the axilla, groin, umbilicus, and other areas.<unk>  generally occurs due to insulin spillover (from excessive production due to obesity or insulin resistance) onto the skin which results in abnormal skin growth 
The most common cause of<unk>  is insulin resistance, usually from type 2 diabetes mellitus.Involvement of mucous membranes is rare and suggests a coexisting malignant condition.
Acanthosis nigricans
Brittle nails
Pitted nails
Xerosis
Hyperpigmentation
Erythema dyschromicum perstans
Moon facies
Xerophthalmia