What lies behind melasma: a review of the related skin microenvironment.

Melasma is an acquired chronic pigmentary disorder affecting millions of individuals worldwide. However, the pathogenesis of melasma remains unclear. This article provides a comprehensive review of the pathophysiological changes occurring in the skin microenvironment of melasma lesions, which can be summarized as follows: (1) skin barrier dysfunction and abnormal synthesis, transport, and intracellular distribution of melanin in the epidermis; (2) basement membrane damage; (3) solar elastosis, vascular changes, senescent fibroblasts, mast cell infiltration, and sebocyte participation in the dermis; and (4) systemic factors such as sex hormones and oxidative stress. Furthermore, potential therapeutic strategies are introduced to provide novel perspectives for fundamental and clinical research related to melasma.