Sulfur-containing amino acid, antioxidant cofactor. Functional formulation ingredient with no standalone activity on the skin.
Topical application
CWeak evidence. In vitro data, open-label studies, or expert consensus.
Inert formulation ingredient. Safe, no standalone activity.
Cysteine is a sulfur-containing amino acid, non-essential in the human body (synthesized from methionine). One of the 20 standard amino acid protein building blocks. The thiol (-SH) group makes cysteine a key antioxidant cofactor. Mechanism in cosmetics. In formulas it acts as a functional ingredient: supplements the amino acid profile, supports the stability of other thiol-containing molecules (e.g., glutathione), can serve as a buffer antioxidant. No standalone topical skin activity – at cosmetic concentrations cysteine is more a structural element of the formula than an active. Where applied. Serums and creams with an 'amino acid complex' marketing angle, products for damaged hair, scalp masks. In Spain – mass-market shampoos labeled 'keratin and amino acids', niche serums with a barrier-restoring focus. Evidence base. Topical clinical data on skin are scarce. On hair, cysteine from keratin hydrolysates partially restores damaged sulfur bonds – confirmed in standard hair-strength tests. No comparable skin data. Safety. CIR confirmed L-cysteine safe in cosmetic use. Hypoallergenic, non-comedogenic. Reactions theoretically possible in patients allergic to sulfur or sulfonamides – extremely rare in practice. Pregnancy and lactation – safe. Cysteine is needed by the body at any life stage; topical cosmetic concentrations don't create issues. Best suited to: damaged hair – yes. For skin it's a filler component; don't expect a standalone effect.
Irritation potential
LowAllergen risk
LowPregnancy
SafeThe Evigrade extension adds an evidence panel to Wildberries, Goldapple, Letu, iHerb, Sephora and 12 more stores. This ingredient and every other one in the product show evidence-tier, allergen risk and pregnancy/lactation flags at a glance.
Cysteine is considered safe during pregnancy at typical cosmetic concentrations. Systemic absorption through the skin is minimal.
Sulfur-containing amino acid, antioxidant cofactor.
The INCI name is Cysteine. It may also appear as: Цистеин.
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