— § 01
What tranexamic acid actually is.
Tranexamic acid (TXA) is a synthetic analogue of the amino acid lysine. Orally it inhibits plasminogen-to-plasmin conversion and slows bleeding — its primary medical use. The dermatology relevance is downstream: plasmin signalling in the keratinocyte drives prostaglandin and arachidonic-acid pathways that, in turn, drive melanogenesis. Inhibit plasmin and you blunt one of the loops that keeps melasma stubborn.
That mechanism is fundamentally different from tyrosinase inhibitors (HQ, arbutin) and from melanosome-transfer inhibitors (niacinamide). It is also why TXA shows benefit on melasma that retinoids and vitamin C alone do not move — UV-driven, hormonally-influenced pigment that depends on the inflammatory loop rather than on direct synthesis.