Acanthosis nigricans (AN) is a skin condition characterized by abnormally increased coloration (hyperpigmentation) and "velvety" thickening (hyperkeratosis) of the skin, particularly of skin fold regions, such as of the neck and groin and under the arms (axillae). Various benign (non-cancerous) forms of AN have been identified in which the disorder may be inherited as a primary condition or associated with various underlying syndromes, an excess accumulation of body fat (obesity), or the use of certain medications (i.e., drug-induced AN). In other instances, AN may occur in association with an underlying cancerous tumor (i.e., malignant AN).
Experts suggest that AN may be a skin manifestation of insulin resistance, which is a condition characterized by impaired biological responses to insulin. Insulin, a hormone produced by the pancreas, regulates blood glucose levels by promoting the movement of glucose into cells for energy production or into the liver and fat cells for energy storage. (Glucose is a simple sugar that is the body's primary source of energy for cell metabolism.) Some clinicians suggest that insulin resistance causes a build-up of the hormone in the blood, and then it finds its way into skin cells. Insulin resistance may be associated with various disorders, including obesity and non-insulin-dependent (type II) diabetes mellitus. In individuals with type II diabetes mellitus, the pancreas produces insulin but the body becomes resistant to its effects, leading to insufficient absorption of glucose and abnormally increased glucose levels in the blood (hyperglycemia) and urine. As a result, there may be a gradual onset of certain symptoms, including excessive urination (polyuria) and increased thirst (polydipsia), and the development of particular complications without appropriate treatment.
