Hydroquinone decreases melanin production by enzymatically inhibiting the conversion of tyrosine to dihydroxyphenylalanine. Tretinoin promotes cornified cell detachment and enhances shedding. Tretinoin increases mitotic activity, thereby increasing loosely adherent corneocyte turnover. Tranexamic acid is a synthetic derivative of the amino acid lysine and binds the five lysine binding sites on plasminogen. This inhibits plasmin formation and displaces plasminogen from the fibrin surface. In melasma, the hypothesized mechanism of action of tranexamic acid includes the shrinkage of dermal vasculature and decreased melanin synthesis by altering the interaction of keratinocytes and melanocytes and decreasing tyrosinase activity.
