Histopathological evaluation of facial melasma treated with oral tranexamic acid alone and in combination with ketotifen

Tranexamic Acid (TA) has demonstrated effectiveness on melasma treatment, and Ketotifen (KET) may inhibit mast cell-mediated melanogenesis. The histologic basis of their depigmenting effects remains unclear. To evaluate histopathological changes from TA with KET over a 3-month treatment. In this randomized, double-blind trial, 50 women with facial melasma were assigned to KET 1 mg plus TA 250 mg (TA/KET group) or TA 250 mg (TA group), every 12 h for 3-months, with broad-spectrum sunscreen. Skin biopsies were performed at baseline and day-90. Primary outcome was epidermal melanin density reduction; secondary outcomes included stratum corneum compaction, solar elastosis, basement membrane disruptions, and counts of mast cells, melanocytes (including pendulum melanocytes), and upper dermal VEGF density. Groups were comparable at baseline. Both showed reduced epidermal melanin without intergroup difference, with unchanged VEGF expression, mast cell and melanocyte count, and stratum corneum parameters. The TA/KET-group presented an increase in epidermal thickness, reduction in solar elastosis, pendulum melanocytes counting, and basal membrane disruptions. The short treatment and follow-up may have limited detection of histologic progression. Toluidine blue, while effective in detecting abundant mast cell populations, may lack sensitivity for precise quantification. PAS staining of the basement membrane may occasionally produce artifactual discontinuities, even when the membrane is structurally intact. Ketotifen was not tested alone. Both interventions led to epidermal melanin reduction. The combination TA/KET induced greater dermal and epidermal remodeling changes that surpassed those with TA alone, showing features associated with photoaging reversal and skin homeostasis restoration.