Licorice root in skincare: glabridin, mechanism, and evidence for hyperpigmentation
A science-based guide to licorice root extract in skincare — glabridin's tyrosinase inhibition mechanism, liquiritin's melanin dispersal effect, anti-inflammatory properties, and how licorice compares to other brightening actives.
· By MedSpot Editorial · 4 min read
Licorice root extract appears in a wide range of brightening and anti-inflammatory skincare products. Unlike many "natural" brightening ingredients, licorice has specific, well-characterized mechanisms and a reasonable evidence base. Here's the science.
What licorice root extract contains
Licorice root (Glycyrrhiza glabra and related species) contains hundreds of compounds. The three most relevant to skincare are:
Glabridin: The primary active in licorice root extract for skin brightening. A flavanone (polyphenol) that inhibits tyrosinase — the rate-limiting enzyme in melanin synthesis — without cytotoxic effects on melanocytes.
Liquiritin: A glycoside that reduces pigmentation through a distinct mechanism — melanin dispersal rather than synthesis inhibition. Liquiritin breaks down melanin clusters in keratinocytes, redistributing the pigment rather than blocking its production.
Licochalcone A: A chalcone with potent anti-inflammatory properties, specifically inhibiting 5-lipoxygenase and cyclooxygenase pathways (similar to NSAID mechanisms). This is the basis for licorice in sensitive/rosacea-adjacent formulations.
The mechanism of action
Licorice root targets hyperpigmentation through two different pathways simultaneously — which is why it's particularly valued for pigmentation treatment:
Pathway 1: Tyrosinase inhibition (glabridin) Tyrosinase converts tyrosine → DOPA → dopaquinone — the committed step in melanin synthesis. Glabridin competitively inhibits tyrosinase, reducing melanin output at the source. Kfurthermore (1998, Pigment Cell Research) demonstrated glabridin inhibited tyrosinase activity by up to 50% at 1 μg/ml in cultured B16 melanoma cells.
Pathway 2: Melanin dispersal (liquiritin) Rather than blocking synthesis, liquiritin acts on existing melanin in keratinocytes. The mechanism: liquiritin appears to accelerate the natural process of melanin dispersion and degradation as keratinocytes migrate toward the skin surface, reducing visible pigment concentration. This is a complementary mechanism to tyrosinase inhibition.
Pathway 3: Anti-inflammatory pigment reduction Post-inflammatory hyperpigmentation (PIH) involves UV and inflammatory triggers upregulating melanocyte activity. Licochalcone A's anti-inflammatory effect reduces one of the key upstream signals driving PIH — reducing future pigmentation formation rather than treating existing deposits.
Clinical evidence
Yokota et al. (1998, Pigment Cell Research): Found glabridin at 0.5% inhibited UV-induced hyperpigmentation in guinea pigs and demonstrated anti-inflammatory activity comparable to hydrocortisone in an ear-swelling assay.
Amer & Mekhail (2000): In a split-face study, 0.5% liquiritin applied twice daily for 4 weeks significantly reduced the severity of melasma compared to vehicle, with improvement continuing at 8 weeks.
Zubair & Mujtaba (2009): A controlled trial comparing liquiritin gel to conventional treatments found comparable efficacy to 4% hydroquinone for melasma improvement over 4 weeks — a meaningful benchmark given hydroquinone is the longstanding gold standard.
Honest calibration: The evidence is more substantial than most natural brightening ingredients but still limited in scale compared to hydroquinone's decades of RCT data. The mechanisms are well-characterized at the cellular level; the clinical data is promising but not definitive.
Licorice root vs. other brightening actives
| Ingredient | Mechanism | Evidence | Irritation | Pregnancy |
|---|---|---|---|---|
| Licorice root | Tyrosinase inhibition + dispersal + anti-inflammatory | Moderate | Low — actually anti-inflammatory | Safe |
| Niacinamide | Melanosome transfer inhibition | Strong | Low | Safe |
| Kojic acid | Tyrosinase inhibition (copper chelation) | Moderate | Moderate (sensitizer risk) | Use caution |
| Azelaic acid | Tyrosinase inhibition + anti-inflammatory | Strong | Low–Moderate | Category B (safe) |
| Tranexamic acid | Plasmin inhibition (UV-melanocyte signaling) | Strong | Low | Avoid oral; topical uncertain |
| Hydroquinone | Tyrosinase inhibition + melanocyte cytotoxicity | Very strong | Moderate — ochronosis risk long-term | Avoid |
| Arbutin | Tyrosinase inhibition (hydroquinone precursor) | Moderate | Low | Use caution |
Where licorice fits: Licorice root is best positioned as a low-irritation brightening active — safe for sensitive skin, rosacea-prone, and pregnancy-adjacent contexts where stronger actives are contraindicated or poorly tolerated. It can also be combined with other brightening actives (niacinamide, azelaic acid) for additive effect.
Concentration and product evaluation
Effective glabridin concentration: Studies used concentrations of 0.1–2% pure glabridin. Most "licorice root extract" products list the extract rather than isolated glabridin — making direct concentration comparison difficult.
How to evaluate:
- "Licorice root extract" standardized to glabridin content (some manufacturers specify %) is more predictable than unstandardized extract
- Position in the INCI list: should be in the first half for meaningful effect
- Look for products specifying which actives are included (some list Licorice Root Extract and also liquiritin separately)
Forms used in skincare:
- Licorice root extract (most common) — full extract, unstandardized
- Glabridin (isolated compound) — more predictable concentration
- DPG (dipotassium glycyrrhizate, from glycyrrhizin) — primarily anti-inflammatory, less effect on pigment
- Licochalcone A — primarily anti-inflammatory (used heavily in Eucerin redness products)
How to use licorice root extract
In routine: Serum step, AM and/or PM. No photosensitivity — licorice extract is safe for AM use without the retinoid or AHA caveats.
Combining with other brightening actives:
- With niacinamide: Complementary mechanisms (tyrosinase inhibition + melanosome transfer inhibition); commonly combined in one formula
- With vitamin C: Compatible; both inhibit melanin via different pathways
- With azelaic acid: Compatible; both have anti-inflammatory + tyrosinase inhibition mechanisms
- With tranexamic acid: Can be combined for comprehensive pigment targeting
Timeline: Expect 8–12 weeks of consistent use before meaningful pigmentation improvement. Hyperpigmentation treatments require consistent application and strict daily SPF.
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