Tranexamic acid is a synthetic derivative from the amino acid lysine. It is often used in combination with polyhydroxy acids to help lighten the skin, although it is just as effective on its own.
Tranexamic acid reduces the level of microphthalmia-associated transcription factor (MITF).
MITF is part of the biological mechanism that helps regulate melanocyte development and differentiation.
It is also involved in the transcription process of melanogenesis enzyme genes, which means if you can reduce MITF activity, you can reduce or limit pigmentation before it starts.