Hair Dye
DIHYDROXYINDOLE
Safety score · 0–100
Moderate
Derived from EU CosIng regulatory status, PubChem hazard data and published research. How we score.
About
A melanin precursor used in gradual/progressive hair dyes. Lower sensitization than traditional dyes, but still a reactive intermediate with caveats.
Dihydroxyindole (CAS 3131-52-0) is an indole-based melanin precursor used in progressive hair-coloring systems. It mimics the natural melanogenesis pathway, polymerizing to form brown/black eumelanin-like pigments upon air oxidation. SCCS has evaluated 5,6-dihydroxyindole and related isomers for hair-dye safety and imposed concentration limits in the EU (typically <=0.5% for non-oxidative hair dye use). Shows positive signal in some in vitro genotoxicity assays though with threshold interpretation debated. Less sensitizing than PPD-class dyes but still a reactive aromatic-system compound. Score sits in Moderate/orange — functional and regulatorily accepted at limited concentration, but with real chemical caveats.
Function
Skin benefits
- Gradual natural-style hair darkening
- No peroxide oxidation required
- Lower sensitization than PPD-class dyes
Known concerns
- Positive in some in vitro genotoxicity assays
- Concentration-limited by SCCS for cosmetic use
- Stains skin and surfaces
- Limited long-term safety data
References
EU CosIng database
European Commission cosmetic ingredient registry — regulatory status, restrictions, authorised functions.
Related hair dyes
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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.