Licorice root skincare guide: glabridin, brightening, and anti-inflammatory evidence

Licorice root (Glycyrrhiza glabra, G. uralensis) is one of the most clinically useful botanical extracts in skincare — containing three distinct active fractions with different mechanisms targeting brightening, anti-inflammation, and barrier support. Understanding which fraction is doing what allows for intelligent product selection. Here is the complete guide.

The three active fractions

Glabridin — the brightening active

Glabridin is an isoflavonoid — the primary brightening compound in licorice root extract. Mechanism:

Tyrosinase inhibition: Glabridin inhibits tyrosinase through a different binding site than kojic acid or alpha-arbutin. It also inhibits dopachrome tautomerase — a downstream enzyme in the melanin synthesis pathway — providing dual inhibition at two steps in the cascade.

UVB-pigmentation inhibition: Beyond tyrosinase inhibition, glabridin prevents UVB-induced melanin synthesis and melanocyte proliferation at concentrations as low as 0.1–1% in cell culture studies. The proposed mechanism involves direct inhibition of UVB-induced tyrosinase activity upregulation.

Evidence: Yokota et al. (1998, Pigment Cell Research) demonstrated that glabridin inhibits UVB-induced pigmentation in guinea pig skin in vivo — one of the key animal model studies establishing licorice root's depigmenting credentials. Multiple subsequent human studies confirm brightening activity.

Liquiritin — an alternative brightening pathway

Liquiritin is a flavanone glycoside in licorice root that brightens through a different mechanism than tyrosinase inhibition: it disperses existing melanin granules within keratinocytes — breaking up melanin clusters and distributing them more diffusely, reducing the intensity of focal hyperpigmentation.

This mechanism is distinct from production inhibition (glabridin, kojic acid, arbutin) — liquiritin addresses existing pigmentation rather than preventing new melanin formation. This is why licorice root has a dual effect: preventing new pigmentation (glabridin) and improving existing hyperpigmentation (liquiritin).

Dipotassium glycyrrhizinate (DPG) — the anti-inflammatory fraction

Dipotassium glycyrrhizinate is the potassium salt of glycyrrhizinic acid — the saponin compound responsible for licorice's sweet taste and its anti-inflammatory activity in skincare.

Mechanism: DPG inhibits 11β-hydroxysteroid dehydrogenase (11β-HSD) — the enzyme that converts inactive cortisone to active cortisol in peripheral tissues. By locally prolonging cortisol activity, DPG mimics mild corticosteroid anti-inflammatory effects without the actual steroid.

Additionally, DPG directly reduces:
Prostaglandin synthesis (COX pathway inhibition)
Histamine release from mast cells
NF-κB-driven cytokine production

Clinical applications of DPG:
Rosacea: DPG's anti-inflammatory and vessel-soothing properties reduce erythema and flushing. Used as an active in rosacea-specific formulations as an alternative to topical azelaic acid in very sensitive skin.
Periorbital hyperpigmentation (dark circles): DPG reduces vascular-driven dark circles through anti-inflammatory mechanisms that reduce the hemoglobin breakdown products (biliverdin, hemosiderin) responsible for blue/purple under-eye coloration.
Post-inflammatory hyperpigmentation: Reducing inflammation reduces the melanogenic stimulus — DPG's anti-inflammatory activity reduces PIH formation.

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Evidence for hyperpigmentation

Melasma

*Amer M, Metwalli M. (2000). Topical liquiritin improves melasma. International Journal of Dermatology, 39(4), 299–301.*

RCT comparing topical liquiritin cream vs. hydroquinone for melasma over 4 weeks — significant improvement in both groups, with liquiritin showing comparable efficacy to hydroquinone (the gold-standard depigmenting agent) with better tolerability.

Multiple subsequent studies confirm licorice root extract (standardized to glabridin content) improves melasma at 10–40% extract concentrations in emulsions.

Comparison to other brighteners

| Brightening Agent | Primary Mechanism | Evidence Level | Irritation Risk |
|---|---|---|---|
| Hydroquinone 4% | Tyrosinase inhibition; melanocyte toxicity | Highest | High (ochronosis risk at long-term use) |
| Alpha-arbutin 2% | Tyrosinase inhibition (competitive) | Strong | Low |
| Kojic acid 1–2% | Tyrosinase copper chelation | Strong | Moderate (sensitization) |
| Tranexamic acid | Plasmin inhibition; keratinocyte-melanocyte signaling | Strong | Low |
| Glabridin (licorice) | Tyrosinase + dopachrome inhibition + melanin dispersal | Moderate | Very low |
| Niacinamide 5% | Melanosome transfer inhibition | Strong | Very low |

Licorice root's positioning: moderate evidence with the lowest irritation risk of any depigmenting active — particularly valuable for sensitive skin, rosacea-prone skin, and Fitzpatrick types IV–VI where irritation from kojic acid would cause PIH.

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Effective concentrations

Glabridin-standardized extracts: Products specifying glabridin content (0.5–2% glabridin in a standardized extract) are more reliable for brightening than products simply listing "licorice root extract" without standardization.

Liquiritin: Typically used at 1–2% in brightening formulations.

DPG: 1–3% in anti-inflammatory and rosacea formulations; found in products specifically targeting redness reduction.

Combined licorice root extract: Many products use a full-spectrum extract at 10–40% concentration, containing all three fractions — providing brightening (glabridin + liquiritin) and anti-inflammatory (DPG) simultaneously.

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Routine integration

AM brightening serum: Licorice root extract pairs well with vitamin C (additive tyrosinase inhibition through different mechanisms) and niacinamide (additive via melanosome transfer inhibition). An AM serum containing all three provides comprehensive anti-pigmentation coverage with low irritation.

Rosacea routine: DPG-containing products (labeled as dipotassium glycyrrhizinate) are compatible with azelaic acid and niacinamide — combining anti-inflammatory mechanisms for rosacea management without the irritation of stronger actives.

Pregnancy: Licorice root extract is generally considered safe for topical use during pregnancy — no systemic absorption concerns at cosmetic concentrations. A preferred alternative to hydroquinone (which is avoided in pregnancy) for brightening.

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