Ergothioneine

Ergothioneine is an antioxidant typically used at low concentrations (commonly ~0.1–1%) and is generally well-tolerated in clinical and consumer use, with low rates of irritation reported. It is not pH-dependent and does not have the keratolytic/exfoliating action that commonly drives stinging in compromised skin. Rare individual reactions are still possible in highly reactive or eczematous patients, so it is best categorized as very gentle rather than inert. Safety Notes: In commercial skincare, ergothioneine is most often used as an antioxidant booster in leave-on serums/creams at low levels around 0.01–0.1%, where it supports formula claims without major solubility/cost burdens. Higher-strength consumer-available products (typically antioxidant serums or concentrated treatments) are observed up to about 0.5–1.0%, which aligns with the upper end seen in marketed “high antioxidant” formulations; rinse-off products generally sit at the low end due to limited contact time.