Carnosine

Carnosine is a naturally occurring dipeptide used in skincare primarily as an antioxidant/anti-glycation agent, typically at low concentrations (about 0.1–1%), and it is generally well tolerated in leave-on products. Available human data and widespread cosmetic use suggest a low rate of irritation or sensitization compared with acids, retinoids, fragrances, or more reactive preservatives. For highly reactive or eczema-prone patients, mild stinging can still occur depending on the overall formula (pH, solvents, other actives), but the ingredient itself is best classified as very gentle. Safety Notes: In commercial anti-aging/anti-glycation serums and moisturizers, carnosine is commonly used at very low levels (around 0.01–0.1%) as a supportive antioxidant/anti-glycation active, and it also appears at these trace levels in some multi-ingredient formulas. Higher-strength consumer-available leave-on treatments (serums/ampoules) have been marketed around ~1–2% carnosine, which is near the practical upper end due to solubility, cost, and formulation constraints; rinse-off products, when they include it, are typically at the low end because of limited contact time. No specific EU/FDA cosmetic maximum is set for carnosine, so the observed range is primarily market- and stability-driven.