Regulatory Status
For full compliance data across 55 jurisdictions, use the Substance Compliance tool.
Safety Data
Calculate MoS for your specific formulation with the MoS Calculator.
Toxicological Studies
4 study endpoints found for L-Cysteine. NOAEL (No Observed Adverse Effect Level) values are used to calculate the Margin of Safety per SCCS methodology.
| Endpoint | Value | Route | Species | Study Type | Source |
|---|---|---|---|---|---|
| NOAEL | 3000 mg/kg bw/day | oral | rat | Short Term Toxicity | COSMOS_DB |
| NOAEL | 200 mg/kg bw/day | oral | mouse | Short Term Toxicity | COSMOS_DB |
| NOAEL | 100 mg/kg bw/day | oral | rat | Subchronic | COSMOS_DB |
| NOAEL | 8000 mg/kg bw/day | oral | rat | Multigeneration Reproductive | COSMOS_DB |
Expert 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.
Regulatory Flags
Frequently Asked Questions
Is L-Cysteine safe in cosmetics?
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. The EU classifies L-Cysteine as "permitted". Safety rating: GOOD. 4 toxicological study endpoint(s) are available in our database.
Is L-Cysteine allowed in the EU?
L-Cysteine EU regulatory status: permitted. This is based on EU Regulation 1223/2009 and its amendments.
What does L-Cysteine do in cosmetics?
L-Cysteine functions as: amino acid; reducing agent; hair-restructuring active; keratin smoothing agent; disulfide bond modulator. It is classified as a Active Ingredient in our database. CAS number: 52-90-4.
What is the Margin of Safety for L-Cysteine?
not established The Margin of Safety (MoS) is calculated using SCCS methodology. A MoS above 100 is generally considered safe. Use the MoS Calculator tool to calculate MoS for your specific formulation and product category.
What is the NOAEL for L-Cysteine?
The NOAEL (No Observed Adverse Effect Level) for L-Cysteine is 3000 mg/kg bw/day based on a Short Term Toxicity study via oral route in rat. A total of 4 study endpoints are available. Source: COSMOS_DB.
Compliance Tools
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Related Ingredients
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