Phenylethyl Resorcinol

Phenylethyl resorcinol is a skin-brightening tyrosinase inhibitor typically used around ~0.1–1% in leave-on products. In clinical and consumer use it is generally well-tolerated, but as a phenolic/resorcinol derivative it can still trigger stinging, redness, or eczema flares in reactive or compromised skin, especially when combined with other actives (retinoids, acids) or in impaired barriers. I score it as mild because irritation is not expected in most users, yet is plausible and clinically relevant in sensitive-skin populations. Safety Notes: In consumer brightening/anti-spot leave-on serums and creams, phenylethyl resorcinol is commonly present at low levels around 0.05–0.2% as a supportive tyrosinase-inhibiting active, aligning with typical supplier guidance and stability/sensory constraints. Numerous OTC dark-spot correctors and specialty pigment products use 0.5% and up to about 1.0% in leave-on formats as the practical high end observed in the market; higher levels are uncommon due to irritation risk and formulation challenges. Rinse-off cleansers, when present, tend to sit at the low end of this range because of short contact time and cost.