Cysteine
INCI: CYSTEINE
CAS 52-90-4 EC 200-158-2 / 222-160-2
L-Cysteine
Limited Data
Insufficient safety data available. Consider enriching this ingredient.
Details
Description
L-Cysteine
Purpose
Function
amino acid; reducing agent; hair-restructuring active; keratin smoothing agent; disulfide bond modulator
Profile
Properties
Silicone
Silicone free
Compliance
Regulatory Status
EU
Permitted
Safety
GOOD
US
Permitted
Absorptionlow
Sensitizationnone
MoSnot established
NOAEL175 mg/kg
ConcernLow
Flags
formaldehyde-freeamino-acid-smoothingendogenousgentledisulfide-modulatorclean-labelprofessional-treatmenteu_children_restrictedfda_food_additivejecfa_safe
Verdict
L-Cysteine is a naturally occurring amino acid that modulates disulfide bond chemistry in hair, used in cysteine-based amino acid smoothing systems as a gentler, formaldehyde-free alternative to traditional keratin treatments and thio relaxers with excellent tolerability and endogenous safety profile.
US Note
Permitted. Used in cysteine-based amino acid smoothing systems as a gentler, formaldehyde-free hair smoothing alternative. Modulates disulfide bonds via amino acid chemistry. No FDA restrictions.
Assessment
Ratings
Reference