Activity evaluation of epidermo-melanin unit and dermal damage in melasma

The study investigated the pathogenesis of melasma, focusing on the interaction between the epidermal-melanin unit and the dermis. It found that melasma involved altered nuclear morphology and chromatin texture in basal keratinocytes, increased expression of αMSH and MC1R, and more mature organelles and melanosomes in keratinocytes and melanocytes. Damage was observed in the basal membrane zone, with more pendulous melanocytes and disorganized dermal collagen. Fibroblasts showed increased SA-β-gal marking and altered gene expression. These findings suggested that melasma's phenotype resulted from changes in the entire epidermal-melanin unit, not just melanocyte hypertrophy, with a potential role for dermal repair/damage processes and fibroblast senescence.