Hair Conditioning
GLYOXYLOYL CYSTEINE
Safety score · 0–100
Moderate
Derived from EU CosIng regulatory status, PubChem hazard data and published research. How we score.
About
Glyoxyloyl cysteine — a hair-straightening active marketed as a formaldehyde-free alternative, but heated-use scenarios can still release formaldehyde.
Glyoxyloyl cysteine is the cysteine conjugate of glyoxylic acid, used in next-generation Brazilian-style hair-straightening treatments that market themselves as "formaldehyde-free" compared to older thioglycolate/formaldehyde systems. However, glyoxylic-acid-based straighteners have been shown to release formaldehyde under the high temperatures of flat-iron / keratin-treatment application, which is a repeatedly documented inhalation-exposure concern in salon settings. No CIR or SCCS monograph covers it yet; regulatory bodies in the US, EU, and Brazil have issued warnings about glyoxylic-acid-based hair smoothing systems.
Function
Skin benefits
- Formaldehyde-free alternative for hair smoothing
- Reversible cysteine-protein binding
- Brazilian-keratin-style straightening claim
Known concerns
- Glyoxylic-acid / glyoxyloyl chemistry can release formaldehyde when heated
- Flat-iron temperatures during use create fume-exposure risk
- Emerging use — no CIR or SCCS monograph
- Scalp irritation reported
References
EU CosIng database
European Commission cosmetic ingredient registry — regulatory status, restrictions, authorised functions.
Related hair conditionings
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This profile is for educational purposes and does not constitute medical advice. Regulatory status and scientific understanding evolve — always read the physical product label and consult a healthcare professional for personal concerns.