Patients with diabetes develop a darkening of the neck, often seen in obese patients, called acanthosis nigricans. Acanthosis nigricans is a cutaneous sign of insulin resistance. High concentrations of insulin bind to insulin-like growth factor receptors on the skin’s acanthocytes and fibroblasts, which stimulate excessive growth of the skin’s acanthocytes and fibroblasts, resulting in the skin changes of acanthosis nigricans, where the skin on the patient’s neck becomes thicker and darker. The skin changes of acanthosis nigricans can precede the onset of diabetes for a long time. The long-term insulin resistance and hyperinsulinemia accompanying acanthosis nigricans can cause pancreatic islet dysfunction, resulting in a relative lack of insulin secretion and abnormal glucose tolerance, which eventually leads to the development of type 2 diabetes.