Melasma: When Dermal Photoageing Precedes Melanocyte Ageing.

Melasma is a chronic relapsing hyperpigmentary disorder with difficult long-term management. In this review, melasma is proposed as a disorder of persistent melanocyte activation sustained within a photoaged dermal microenvironment. This microenvironment, composed of senescent fibroblasts, UV-activated sebocytes and vascular components, functions as a dermal melanogenic field that continuously provides melanogenic signalling. We further propose that melasma may arise within a melanogenic window, a phase characterized by a photoaged dermis and melanocytes that remain responsive to melanogenic stimulation. This window may result from dermal ageing preceding melanocyte ageing. This asynchronous cellular ageing may explain the characteristic midlife onset, chronic relapsing course and later life attenuation of melasma. From a therapeutic perspective, effective long-term management of melasma may require not only suppression of persistent melanocyte activation but also modulation of the photoaged dermal microenvironment.