Lysine Carboxymethyl Cysteinate

Lysine Carboxymethyl Cysteinate is a water-soluble amino acid/thiol derivative primarily used as an antioxidant/conditioning agent, typically at low concentrations in leave-on formulas. Available safety and use-history data for similar amino-acid derivatives suggest low intrinsic irritation and minimal sensitization risk, though the cysteine/thiol functionality can rarely contribute to stinging in highly compromised skin. Given its generally gentle profile but non-zero potential in eczema/post-procedure barriers, a very gentle score is most consistent with patient safety. Safety Notes: In commercial skincare, Lysine Carboxymethyl Cysteinate is typically used as an antioxidant/anti-dark-spot supportive active (often within complex blends), with low-end usage around 0.05–0.2% in leave-on serums/creams where it functions as a secondary supporting ingredient. Higher-strength consumer-available brightening/anti-oxidative leave-on treatments have been observed around 0.5–2.0% when positioned as a primary active or key complex component; above ~2% is uncommon due to diminishing formulation practicality (odor/color, solubility, and stability constraints). Rinse-off products generally sit at the lower end because of reduced contact time and cost/performance tradeoffs.