What Is Stearyl Glycyrrhetinate? Technical Brief, Anti-Inflammatory Data, and Formulating Oil-Soluble Licorice Derivatives
ステアリルグリチルレチネート is the lipophilic ester derived from 18β-glycyrrhetinic acid and stearyl alcohol. While water-soluble licorice extracts like Dipotassium Glycyrrhizate dominate aqueous serums, they struggle to penetrate the hydrophobic stratum corneum. Esterifying glycyrrhetinic acid with a C18 fatty chain solves this limitation. The result is a lipid-compatible active ingredient designed for anhydrous systems, emulsions, and lipid-barrier repair formulas.
Chemical Profile and Molecular Structure
- INCI名： ステアリルグリチルレチネート
- CAS Number: 13832-70-7
- EINECS/ELINCS Number: 419-580-5
- Molecular Formula: C48H82O4
- 分子量： 723.16 g/mol
- Chemical Structure: 18β-glycyrrhetinic acid 30-stearyl ester
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[ Glycyrrhetinic Acid Core ] — C(=O)—O—(CH2)17—CH3
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O=C
Natural 18β-glycyrrhetinic acid contains a carboxylic acid group at the C-30 position. Esterification at C-30 with octadecanol (stearyl alcohol) increases lipophilicity (Log P = 6.2). This change facilitates passage through intercellular epidermal lipids. Once inside the stratum corneum, endogenous esterases gradually cleave the ester bond, releasing free glycyrrhetinic acid for sustained biological activity.
Standard Certificate of Analysis (COA) Specifications
The following table outlines the industrial raw material quality control criteria for cosmetics manufacturing:
| Testing Item | 仕様標準 | 通常のバッチ結果 | 試験方法 |
|---|---|---|---|
| 外観 | 白色～オフホワイトの結晶性粉末 | 白い微粉末 | Visual inspection |
| 臭い | Characteristic faint odor | Conform | Olfactory |
| Purity (Assay by HPLC) | ≥ 98.0% | 61% | HPLC (C18 column, UV 254 nm) |
| 融点 | 70.0 °C – 77.0 °C | 73.5 °C – 75.0 °C | Capillary melting point apparatus |
| 乾燥減量 | 105℃、2時間 | 0.35% | 105 °C, 2 hours |
| 燃焼残渣 | ≤ 0.2% | 0.08% | Ignition at 600 °C |
| 重金属（鉛として） | 鉄（Fe） | 5 ppm未満 | ICP-MS |
| ヒ素（As） | ≤ 2 ppm | 1 ppm未満 | AAS |
| Microbiological Testing | Total Plate Count < 100 CFU/g | 10 CFU/g未満 | ISO 21149 / ISO 16212 |
Solubility Profile & Solvent Compatibility
Unlike salt forms of glycyrrhizic acid, Stearyl Glycyrrhetinate is virtually insoluble in water (9 μg/L at 20 °C). It requires dissolved lipid carriers or warm organic solvents.
| Solvent / Lipid Phase | Solubility at 25 °C | Solubility at 75 °C | 製剤に関する注記 |
|---|---|---|---|
| 水 | Insoluble | Insoluble | Unsuitable for direct aqueous phase |
| Ethanol (95%) | Slightly soluble | Soluble (~2.5%) | Precipitates if cooled rapidly in pure state |
| Caprylic/Capric Triglyceride (MCT) | ~0.8% w/w | > 5.0% w/w | Ideal carrier oil for pre-dissolution |
| スクワラン | ~0.5% w/w | > 4.0% w/w | Excellent lipid base for facial oils |
| Mineral Oil / Isohexadecane | ~0.4% w/w | ~3.5% w/w | Good compatibility in hydrocarbon systems |
| Jojoba Oil / Plant Oils | ~0.3% w/w | > 3.0% w/w | Requires heating above 75 °C to dissolve |
Biological Mechanisms & In-Vitro Performance Data
Stearyl Glycyrrhetinate modulates inflammatory cascades primarily by inhibiting 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) and downstream arachidonic acid pathways.
1. Inhibition of Pro-Inflammatory Mediators
Inflammatory stressors (UV radiation, chemical irritants, surfactant disruption) activate phospholipase A2. This enzyme releases arachidonic acid, converting it to prostaglandin E2 (PGE2) via cyclooxygenase-2 (COX-2).
In HaCaT Cell Culture Assays (stimulated with LPS 1 μg/mL):
- PGE2 Suppression: IC50 value of 12.4 μM (vs. 28.6 μM for Dipotassium Glycyrrhizate).
- Interleukin-6 (IL-6): Reduces IL-6 secretion by 54.2% at 20 μM.
- TNF-α: Suppresses expression by 41.8% at 20 μM.
2. Antimicrobial Benchmarks (MIC Values)
Broad-spectrum antimicrobial activity helps stabilize acne-prone and compromised skin microflora. Standard broth microdilution testing yields the following Minimum Inhibitory Concentrations (MIC):
- Cutibacterium acnes (ATCC 6919): MIC = 62.5 μg/mL
- Staphylococcus aureus (ATCC 6538): MIC = 125 μg/mL
- Staphylococcus epidermidis (ATCC 12228): MIC = 250 μg/mL
3. In-Vivo Erythema Reduction Study
A randomized split-face clinical test measured erythema reduction following sodium lauryl sulfate (SLS, 2% patch) irritation. Twenty subjects applied a formulation containing 0.2% Stearyl Glycyrrhetinate versus a placebo vehicle twice daily.
- Day 3: Skin redness decreased by 31.4% relative to baseline (measured via spectrophotometer a* value).
- Day 7: Redness decreased by 68.9%, with Trans-Epidermal Water Loss (TEWL) recovering 42% faster プラセボ群と比較して。
Formulating with Stearyl Glycyrrhetinate
Why choose Stearyl Glycyrrhetinate over traditional licorice salts? High concentrations of ionic salts like Dipotassium Glycyrrhizate can destabilize emulsion systems or break polymeric thickeners (such as Carbomer or Acrylates/C10-30 Alkyl Acrylate Crosspolymer). Stearyl Glycyrrhetinate is non-ionic and lipophilic, making it completely neutral to emulsion viscosity.
Phase Processing and Heating Requirements
- Add Stearyl Glycyrrhetinate directly to the polar or medium-polar oil phase (MCT, C12-15 Alkyl Benzoate, or Squalane).
- Heat the oil phase to 75 °C – 80 °C under moderate stirring until the powder dissolves completely into a clear liquid.
- Perform emulsification with the water phase at equal temperature.
- If cooling down rapidly, ensure the oil phase has enough solubilizing esters to prevent re-crystallization below 45 °C.
Suggested Dosage Matrix
| Application Type | 推奨使用レベル | 主要機能 |
|---|---|---|
| Barrier Repair Creams & Balms | 0.1% – 0.5% | Soothing, anti-redness, lipid replenishment |
| Lip Balms & Lipsticks | 0.2% – 1.0% | Chapped lip repair, anti-inflammatory support |
| Sunscreen & After-Sun Care | 0.1% – 0.3% | Counteracting UV-induced erythema |
| Anhydrous Serums & Facial Oils | 0.05% – 0.2% | Daily calming for sensitive skin |
| Acne & Blemish Spot Treatments | 0.2% – 0.5% | Reducing localized inflammatory papules |
Synergistic Active Combinations
- Bisabolol (0.2%) + Stearyl Glycyrrhetinate (0.1%): Combined inhibition of both 5-LOX and COX-2 pathways.
- Ceramide NP (0.1%) + Stearyl Glycyrrhetinate (0.2%): Rebuilds intercellular lipids while reducing sub-clinical barrier inflammation.
- Tocopherol (0.5%) + Stearyl Glycyrrhetinate (0.1%): Protects lipophilic active ingredients from oxidation while preventing squalene peroxidation on skin.
Comparative Analysis: Stearyl Glycyrrhetinate vs. Dipotassium Glycyrrhizate
| 特性 | ステアリルグリチルレチネート | グリチルリチン酸ジカリウム |
|---|---|---|
| 溶解度 | Oil-soluble / Lipophilic | Water-soluble / Hydrophilic |
| Log P Value | 6.2 | < -1.5 |
| Skin Penetration Target | Stratum corneum & lipid matrix | Epidermal aqueous intercellular space |
| Impact on Viscosity | No effect on emulsion rheology | Can lower carbomer / gel viscosity at > 0.5% |
| 熱安定性 | Stable up to 85 °C in oil phase | Stable up to 80 °C in water phase |
| Ideal Product Format | Lipsticks, rich creams, oils, sunscreens | Toners, gels, sheet masks, aqueous serums |
Regulatory Status and Safety Assessment
- US CIR (Cosmetic Ingredient Review): Assessed as safe for use in cosmetic formulations up to 1.0%.
- EU SCCS / CosIng: Listed without specific restriction (Ref No: 38334); standard cosmetic safety limits apply.
- China NMPA (IECIC): Included in the Inventory of Existing Cosmetic Ingredients in China.
- Japan (Quasi-Drug Active): Approved as an active ingredient for anti-inflammatory and soothing claims within specified limits (0.1% – 0.5%).
Phototoxicity and sensitization studies confirm that Stearyl Glycyrrhetinate exhibits zero phototoxic potential at 1.0% concentration. It passes standard Human Repeat Insult Patch Tests (HRIPT) with no observed irritation.
Packaging, Storage, and Handling
- パッケージ： Standard industrial supply comes in aluminum foil bags or fiber drums lined with double-layer polyethylene bags.
- 保管条件： Keep containers tightly sealed in a cool, dry, and ventilated place (15 °C – 25 °C). Protect from direct sunlight and moisture.
- 貯蔵寿命： 24 months from manufacturing date when stored in unopened original containers.
- Sample Requests: Pure grade production samples are available for research and R&D formulation trials upon request.
Literature & Scientific References
- Cosmetic Ingredient Review Expert Panel. (2007). Final Report on the Safety Assessment of Glycyrrhetinic Acid, its Salts, and Esters. International Journal of Toxicology, 26(Suppl 2), 79–112.
- 柴田、S. (2000)。 A review of the anti-inflammatory actions of licorice and its active compounds. Journal of the Pharmaceutical Society of Japan, 120(10), 849–862.
- Finney, R. S. H., & Somers, G. F. (1958). The anti-inflammatory activity of glycyrrhetinic acid and its derivatives. Journal of Pharmacy and Pharmacology, 10(1), 613–620.
- Yokota, T., Nishio, H., Kubota, Y., & Mizoguchi, M. (1998). The inhibitory effect of licorice extract on melanogenesis and inflammation. Pigment Cell Research, 11(6), 355–361.
- Inagaki, N., et al. (2006). Inhibitory effects of 18β-glycyrrhetinic acid derivatives on immediate and delayed-type hypersensitivity reactions. Biological and Pharmaceutical Bulletin, 29(8), 1734–1739.
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