Cysteine
AKA: L-cysteine, (R)-2-Amino-3-mercaptopropanoic acid, Thioserine, Half-cystine
Synthetic
Antioxidant
Skin Conditioner
Hair Care
Amino Acid
Medicated Active
Clean
L-Cysteine
Formula
C3H7NO2S
Mol. Weight
121.16
CAS #
52-90-4, 3374-22-9
Form
Powder
Functions
Antioxidant
Fights free radicals — the unstable molecules from UV, pollution, and stress that break down collagen and cause premature aging.
Antistatic
Hair Conditioning
A catch-all term for ingredients that improve how skin looks and feels — softer, smoother, more supple. The workhorse behind most moisturizers.
Hair Waving Or Straightening
Reducing
Neutralizes Free Radicals
Traditional Use
An amino acid first isolated in 1810. Discovered to support keratin formation in hair and skin; used since the 1970s-1980s in anti-aging and hair strengthening formulations for its role in collagen and glutathione synthesis.
Skin Types
●all-skin-types
Best For
General
Pregnancy & Breastfeeding Safe
Yes
The paper trail
🔬Peer-reviewed1 paper →
⚖️Regulatory1 listing →
🛡️Safety-assessed2 reviews →
Counts, not a verdict. A listing isn't a study. The trail, you decide.
Verified Jun 2026
Data: PubChem · CosIng · EWG · CIR