Stearyl glycyrrhetinate is an ester of glycyrrhetinic acid, the compound responsible for much of licorice root's anti-inflammatory reputation, joined to stearyl alcohol.
Where it comes from
Licorice root contains glycyrrhizin, which is metabolised to glycyrrhetinic acid, also called enoxolone. That compound has been used in dermatological preparations for irritated skin for decades and is among the better-evidenced botanical-derived anti-inflammatories in topical use.
Why the ester rather than the acid
Glycyrrhetinic acid is poorly soluble in both water and oil, which makes it awkward to formulate. Attaching a stearyl chain makes the molecule oil-soluble and compatible with emulsions and anhydrous bases.
As with all esters, skin enzymes must cleave it to release the active compound, so delivery is more gradual and, as always, partial.
How it works
The proposed mechanism is interesting and specific. Glycyrrhetinic acid inhibits 11-beta-hydroxysteroid dehydrogenase, the enzyme that inactivates cortisol in tissue. By slowing that inactivation, it prolongs the effect of the body's own cortisol locally.
This is described as a corticosteroid-sparing or steroid-mimetic effect. It is not a corticosteroid and does not carry the risks associated with topical steroid use, but it acts on the same signalling pathway from a different direction.
There is also documented direct anti-inflammatory activity and inhibition of inflammatory mediators.
Where it appears
Frequently in formulations where irritation is expected: exfoliants, retinoid products, after-sun and post-procedure care. Also common in products for sensitive or reactive skin.
Its presence in a formula is usually a sign the formulator anticipated the product might sting, which is a reasonable thing to notice when reading an ingredient list.
Safety
Well tolerated at cosmetic concentrations. The blood pressure and potassium effects associated with eating large quantities of licorice relate to systemic glycyrrhizin from ingestion and do not apply to topical cosmetic use.
