Beyond the boundaries of pigmentation and inflammation: understanding the mechanistic basis of melasma-rosacea comorbidity.

Melasma and rosacea are common chronic facial dermatoses traditionally regarded as discrete clinical entities. Melasma is primarily characterized by dysregulated melanogenesis and aberrant pigmentary control, whereas rosacea is defined by inflammatory dysregulation and vascular hyperreactivity. However, accumulating clinical observations and experimental evidence increasingly challenge this conventional separation, revealing substantial overlap in their epidemiologic profiles, triggering factors, histopathological features, and underlying molecular signaling pathways. In this review, we synthesize emerging data that support a unified pathogenic framework for melasma-rosacea comorbidity, conceptualizing these conditions not as isolated disorders but as interconnected phenotypic manifestations arising from shared pathobiological substrates. We particularly emphasize convergent mechanisms involving neurovascular dysregulation, inflammatory cascades, barrier impairment, and pigment-vascular crosstalk, which collectively may account for their frequent coexistence and overlapping clinical features. Meanwhile, we discuss the therapeutic implications of this comorbidity model, highlighting tranexamic acid and other agents with anti-inflammatory and pigment-modulating properties. In this review, we aim to systematically synthesize and critically evaluate current evidence on the association between melasma and rosacea, and to propose a unified pathogenic framework underlying their comorbidity.