The ingredient, explained

Cysteine

Cysteine has a published cosmetic safety assessment.

AntioxidantAntistaticHair conditioningHair waving or straighteningMaskingReducing

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Ingredient guide

What it is and what it does

L-Cysteine

About this ingredient: EU CosIng ingredient registry (via Open Beauty Facts taxonomy) ↗

Antioxidant: Limits oxidation, including deterioration of formulation ingredients. This label alone does not show a clinical antioxidant effect in skin.
Antistatic: Reduces the build-up of static electrical charge on surfaces.
Hair conditioning: Improves cosmetic hair properties such as softness, shine or combability.
Hair waving or straightening: Changes hair structure to allow waving or straightening.
Masking: Reduces or conceals the formula's underlying odour or taste.
Reducing: Chemically changes another material through reduction.

Function definitions: European Commission ingredient function definitions (SCCNFP/0299/00, pages 16 to 20) ↗

Registry functions describe possible formulation roles, not results for a finished product. A dictionary entry is not an approval or a safety assessment.

A closer look

What the research shows

Safety assessment

The report reviews irritation and sensitization evidence relevant to the named amino acids in topical cosmetics.

What this does not tell us

Grouped assessment includes read-across and combination formulations; this is safety evidence, not individual skin efficacy or an oral supplementation recommendation.

Sources for this summary. PubMed 24335967 ↗

Research review checked Oct 1, 2026

Selective screening of 7 local candidates and reuse of the final primary report after checking its explicit exact member list.

Ingredient research is not proof that a product containing this ingredient works.