Plasmin, a kind of protease in the blood serum, functions to enhance the intracellular release of arachidonic acid, a precursor of prostanoid, and also to elevate alpha-melanocyte stimulating hormone processed from pro-opiomelanocortin.

Both arachidonic acid and alpha-melanocyte stimulating hormone can activate melanin synthesis by melanocytes. Therefore, the anti-plasmin activity of tranexamic acid is thought to play a role in its topical effectiveness for treating melasma.

Tranexamic acid is known as an oral medicine for treating melasma. Its rare but severe side effects when taken orally, such as pulmonary embolism, deep-vein thrombosis, myocardial or cerebrovascular infarction, make risky its systemic use in dermatology.