Detailed answer

Hyperpigmentation is often a characteristic feature of adrenal insufficiency, specifically Addison's disease. This condition leads to insufficient production of adrenal hormones, particularly cortisol. The overproduction of adrenocorticotropic hormone (ACTH) in response to the low cortisol levels stimulates the production of melanocyte-stimulating hormone (MSH), which leads to increased melanin production and subsequent hyperpigmentation. The hyperpigmentation tends to occur in areas exposed to sunlight, such as face, neck, and hands. However, it is important to note that not all cases of hyperpigmentation are caused by adrenal insufficiency, as there are various other factors that can contribute to the development of hyperpigmentation, such as sun exposure, hormones, medications, and skin conditions.