Identity
Glabridin is an isoflavan — a polyphenol — and the principal brightening active of licorice root (Glycyrrhiza glabra). It is used under the INCI name Glabridin, or as a standardised Glycyrrhiza Glabra Root Extract. This card exists because the register already carries dipotassium glycyrrhizate — licorice''s soothing salt — and that entry explicitly says the plant''s tone-evening evidence attaches to glabridin, not to the glycyrrhizate. Glabridin is that molecule.
Mechanism (as proposed)
Glabridin inhibits tyrosinase — the enzyme that makes melanin — and separately carries anti-inflammatory activity. That dual action is why licorice earned its reputation both as a brightener and a soother, and why glabridin specifically is credited with the pigment side. The mechanism is genuine and well described in the lab. The honest limiter is practical: glabridin is expensive, poorly water-soluble, and penetrates skin variably, so the concentration that actually reaches living skin in a real product is often modest.
Reading the evidence honestly
There is real human topical data for licorice/glabridin reducing the appearance of pigmentation, but it is modest in size and often from combination formulations, which is why the grade sits at C rather than higher. Two boundaries keep this entry honest. First, glabridin is a distinct thing from dipotassium glycyrrhizate — the same plant, different molecules, different lanes (brightening vs soothing) — and the two should not be conflated. Second, as with every brightener in this register, the measured endpoint is the appearance of existing pigment, not a lightening of baseline skin colour.