Depigmenting Agents: Kojic, Arbutin, Tranexamic

Peels clear pigment that is already there; depigmenting agents stop the skin making more. In melanin-rich skin, where melasma and PIH relapse readily, that second job is half the battle — which is why kojic acid, arbutin and tranexamic acid are core peel adjuncts rather than optional extras. Each intervenes at a different point in the melanin pathway: kojic and arbutin throttle tyrosinase, the rate-limiting enzyme of melanogenesis, while tranexamic acid works further upstream on the plasmin–vascular signalling that drives melasma. Used together with peeling, they consolidate results and lengthen the relapse-free interval.

The pathway you are trying to slow

Melanin synthesis (melanogenesis) runs inside the melanocyte on a single rate-limiting enzyme: tyrosinase, a copper-dependent enzyme that converts tyrosine to DOPA and onward to melanin. Most topical depigmenting agents are, at heart, tyrosinase inhibitors — they slow the assembly line at its bottleneck. A second axis matters specifically in melasma: vascular and hormonal signalling (via plasmin and downstream mediators) upregulates melanocyte activity, which is the lever tranexamic acid pulls.

Kojic acid — copper chelation

Kojic acid inhibits tyrosinase by chelating the copper ion the enzyme needs to function. Remove the cofactor and the enzyme slows. It is a well-established, effective depigmenter and a common component of peel and yellow-peel formulations (it is one of the actives in many combination depigmenting peels). Its main liability is irritation and sensitisation at higher concentrations or with prolonged use — relevant in reactive Fitzpatrick IV–VI skin, where irritation can itself seed PIH — so it is best used at sensible concentrations and combined rather than pushed hard alone.

Arbutin — the gentler tyrosinase brake

Arbutin is a glycosylated hydroquinone — hydroquinone with a sugar attached — that releases its activity gradually and acts as a competitive tyrosinase inhibitor. Because the active is delivered slowly, arbutin is gentler and better tolerated than free hydroquinone, with a more favourable irritation profile. That tolerability makes it attractive in darker skin and for maintenance, where it suppresses new pigment with little inflammatory cost. It is a steadier, lower-risk brake than kojic acid, if a milder one.

Tranexamic acid — a different lever

Tranexamic acid (TXA) is the conceptual outlier: it is not primarily a tyrosinase inhibitor. It is an antifibrinolytic that blocks plasminogen activation, and in skin this dampens the plasmin-driven, vascular and inflammatory signalling that upregulates melanocytes in melasma. By acting upstream of tyrosinase — on the demand signal rather than the enzyme itself — it complements kojic and arbutin rather than duplicating them, which is why TXA (topical, and in selected cases systemic under appropriate supervision) has become a mainstay specifically for melasma.

How they work as peel adjuncts

The peel and the depigmenter are a division of labour, not rivals:

• The peel removes existing pigment — accelerating turnover to shed melanin-laden corneocytes and improving penetration of topicals by thinning the stratum corneum.
• The depigmenter suppresses new pigment between sessions, holding the gains and preventing rebound.
• Sequencing matters. Depigmenters are commonly used to prime before a pigment peel (priming a melasma patient lowers the chance the peel itself triggers PIH) and as maintenance afterward to extend the result. Many depigmenting peels also co-formulate these actives (kojic with AHAs and a retinoid, for example) so the synthesis-blocking and exfoliating actions arrive together.

This adjunctive logic is central in Fitzpatrick IV–VI: because melasma and PIH are relapsing conditions in this population, the maintenance depigmenter is what converts a good post-peel result into a durable one.

A note on hydroquinone: it remains the reference tyrosinase inhibitor but carries exfoliative-dermatitis and, with prolonged use, ochronosis concerns, so kojic, arbutin and tranexamic acid are valued partly as better-tolerated alternatives and rotation partners — important when treatment runs for months in darker skin.

Key takeaway

Depigmenting agents stop the skin making new pigment while the peel clears what is already there. Kojic acid and arbutin both inhibit tyrosinase — kojic by chelating its copper cofactor, arbutin as a gentler competitive inhibitor — while tranexamic acid works upstream on the plasmin–vascular pathway that drives melasma. As peel adjuncts they prime before and maintain after, and in Fitzpatrick IV–VI, where melasma and PIH relapse readily, that maintenance is what makes a pigment result durable. Choose by tolerability and pathway, rotate to spare the skin over long courses, and treat pigment as managed, not cured.