ABSTRACT

Hyperpigmentation is a complex process that occurs in physiologic and pathologic states in response to complex signaling cascades and a variety of stimuli, including ultraviolet (UV) radiation, inflammation, hormones, and medications. Hypermelanosis is a pathologic state in which there is an increase of melanin as a result of an increased number of melanocytes in the epidermis or an increased production of melanin. Globally, alterations in pigmentation are a result of genetic defects, hormonal changes, and/or UV radiation. For example, melasma, a disorder of hyperpigmented patches on the face and less commonly dorsal forearms, is thought to be a result of a combination of these factors. Hypermelanosis can be classified clinically and histologically into epidermal and dermal subtypes. Several signaling pathways have been found to play a role in the synthesis, differentiation, and survival of melanocytes. Microphthalmia-associated transcription factor (MITF) is a key transcription factor in upregulating the expression of tyrosinase and stimulating melanogenesis.